From the outset, President Trump’s refrain on the investigation of Russian interference in the 2016 presidential campaign and any coordination with his campaign has been consistent. Since May 2017 — shortly after Robert S. Mueller III was appointed special counsel to investigate the issue — Trump has tweeted some variant of “no collusion!” no fewer than 65 times. That refrain has been constant despite the evolving nature of the investigation, the myriad indictments and the sprawling assessments of who in Trump’s orbit knew what and when.

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In reality, the question of collusion isn’t clear. At the poles are those who insist it is: On one end, there are those who, like Trump, seize on the uncertainty or on truncated investigations run by congressional Republicans to say that the absence of proof is proof of absence; and on the other are Trump critics who point to events such as the June 9, 2016, meeting at Trump Tower as proof of collusion in and of itself. In the middle is a lot of gray, no clear line from Trump’s campaign to the Russians seeking to get him elected.

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Such a line may emerge. If it does, here are five places it might show up, listed in order from most to least likely.

Paul Manafort’s interactions with Konstantin Kilimnik

What we know: We know that, while serving as Trump’s campaign chairman for several months in the middle of 2016, Manafort had repeated email and in-person conversations with Kilimnik, a longtime business partner of Manafort’s who is believed to have links to Russian intelligence. That includes, among many other things, an in-person meeting in early August 2016 down the street from Trump Tower in New York that included Manafort’s business partner Rick Gates (who was also Manafort’s deputy on the campaign).

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To some extent, this is a fairly simple point of interaction to identify as significant because a lawyer working for Mueller himself said that the Manafort-Kilimnik interactions and that Aug. 2 meeting in particular get “very much to the heart of what the Special Counsel’s Office is investigating.”

That comment came in a heavily redacted document detailing a hearing between Mueller’s team and Manafort’s attorneys in which a judge was asked to evaluate the extent to which Manafort might have lied to federal investigators. Those redactions include most of the details about what was discussed during that August meeting, leaving only that tantalizing sentence from attorney Andrew Weissmann.

But journalist Marcy Wheeler, who has been tracking the Mueller inquiry from the outset, matched other released details about Manafort’s time on the campaign to come up with a convincing argument: It was at the Aug. 2 meeting that Manafort shared polling data with Kilimnik, detailed data that came from the campaign.

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When the revelation that polling data had been shared with Kilimnik emerged last month, it reportedly consisted largely of publicly available information and was shared in the spring of 2016, according to a person who spoke with the New York Times. If Wheeler’s theory is correct, the polling came much later and was much more closely linked to the campaign. (I noted in January that the campaign didn’t start logging polling expenses until late August, putting this sharing a bit closer to a feasible time frame.) The reports compiled by former British intelligence officer Christopher Steele that eventually formed an infamous dossier included the specific allegation that, before his ouster from the campaign, Manafort was the point person on a partnership between Trump’s team and the Russians. This has not been publicly substantiated.

Manafort passing proprietary polling data from the campaign to a Russian with connections to Russian intelligence specifically to be shared with oligarchs linked to Russian President Vladimir Putin (as the Times also reported) would indeed get to the heart of what Mueller is trying to uncover.

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Why skepticism is warranted: There are other reasons Manafort might have wanted to share that data. In another conversation with Kilimnik, Manafort asked how he might use his position with the campaign to “get whole” — to recoup money he was owed from former partners in Russia. Manafort had access to something of value and might conceivably have intended to use that to prime the pump. (This raises the ancillary question of whether collusion with Russia needed to have been intentional, which we’ll leave for another day.)

It’s also worth noting that the suggestion that Kilimnik has ties to Russian intelligence doesn’t necessarily mean that the information he was given was shared with those groups.

More compelling is the lack of evidence that any well-targeted effort was undertaken by Russian actors. Data released by social media companies has shown a broad effort to sow division in U.S. politics and to undermine Trump’s 2016 opponent, but we’ve seen no real evidence that there was the sort of targeted effort that might be undertaken with detailed polling data to persuade specific voters in specific places to take a particular action.

In other words, if this was the collusion, it’s not clear how it affected what the Russians were doing.

Roger Stone and WikiLeaks

What we know: Longtime Trump adviser (and temporary Trump campaign adviser) Roger Stone claimed repeatedly during the 2016 campaign to have ties to WikiLeaks, an assertion that he clearly made in part to chuff up his own importance. In the days before WikiLeaks released emails stolen from Hillary Clinton’s campaign chairman, John Podesta, Stone repeatedly hinted at an upcoming document dump. In late August, he had even tweeted that “it will soon the Podesta’s time in the barrel,” a tweet that suggested he knew that dirt on Podesta would soon drop.

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An indictment from Mueller’s team lays out how WikiLeaks obtained information from hackers believed to be linked to Russia. When the hackers first started releasing material stolen from the Democratic National Committee in June 2016, WikiLeaks offered to host future dumps. Material was transferred to WikiLeaks in July; the organization started publishing DNC material shortly before the Democratic National Convention that month.

Stone’s known connections to WikiLeaks come through two former friends of his, a conspiracy theorist named Jerome Corsi and a radio host named Randy Credico. Corsi, in a book released shortly after he rose to national attention because of the Mueller investigation, makes a remarkable claim: That Stone heard that The Post was going to publish the “Access Hollywood” tape on October 7, 2016, and pressed Corsi to tell WikiLeaks to dump the Podesta emails after the tape came out.

That’s essentially what happened. There are other points of overlap between Stone and a Russian believed to be working for that country’s intelligence firms, but the Corsi allegation is the most suggestive of direct coordination.

Why skepticism is warranted: First of all, neither Corsi nor Stone is a particularly reliable narrator, so it’s worth a liberal application of salt to what’s outlined above.

But it’s also very indirect. This is Stone reportedly asking Corsi to ask his guy (apparently an author named Ted Malloch) to press WikiLeaks to release documents at a particular time and WikiLeaks doing so. Making this even more indirect is that Stone didn’t work for the campaign, although the Corsi story does suggest that he was close enough to the campaign to get a heads-up on the “Access Hollywood” tape’s emergence. (The Post contacted the campaign for comment before publishing.)

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On the other side, the link is also indirect. It has not been demonstrated publicly that WikiLeaks knew the material came from Russia or that WikiLeaks, on its end, would have coordinated with Russia about how or when to publish any information.

The Trump Tower meeting

What we know: Donald Trump Jr., Manafort and Trump’s son-in-law, Jared Kushner, met with a lawyer linked to the Kremlin and her colleague, who once worked for the intelligence service in the former Soviet Union. They took the meeting under the understanding that the lawyer had derogatory information about Clinton.

Trump Jr. has repeatedly offered incomplete or inaccurate information about what happened. He told congressional investigators that he didn’t remember having called Manafort and Kushner before scheduling the meeting or talking to a Russian developer named Emin Agalarov, who was the conduit to the lawyer. (Agalarov did remember it.) Trump Jr.'s initial statement about the meeting — drafted by the president — was entirely misleading about the intent of the interaction.

All parties who were involved claim that the discussion largely focused on Russian frustration with a law imposing sanctions following the death of a whistleblower in a Russian jail. (This is reinforced by notes Manafort turned over to investigators.) But this was the most high-level interaction between Trump’s campaign and Russian actors, predicated on the idea that Russia wanted to aid Trump’s effort. This may have been a jumping-off point for the relationship, not a dead end.

Why skepticism is warranted: But there’s no public evidence that it was.

The argument can (and has) been made that the meeting in and of itself is collusion. If your definition of collusion demands a more robust interaction between the two sides, there’s not much available here to support that narrative.

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The campaign advisers

What we know: Two campaign advisers, George Papadopoulos and Carter Page, had interactions with Russians in 2016 that were uncovered by investigators.

Papadopoulos first encountered a London-based professor with connections to Russia who, in April 2016, informed him that the Russians had dirt — emails — incriminating Clinton. (When Papadopoulos allegedly told an Australian diplomat about these emails the following month, the comment made its way back to the FBI, prompting the first investigation of collusion in late July 2016.) Papadopoulos also had an ongoing conversation with a Russian linked directly to Russia’s Ministry of Foreign Affairs, ostensibly to set up a possible meeting between Trump and Putin.

Page traveled to Russia in early July 2016, where he had a conversation with a deputy prime minister, a detail that emerged only after congressional investigators interviewed Page. That included discussion of an email Page sent to the campaign in which he said the deputy prime minister had “expressed strong support for Mr. Trump.”

Why skepticism is warranted: Papadopoulos agreed to cooperate with Mueller’s team in exchange for a lighter prison sentence. He has now served his time. It’s not clear whether Page is a subject of Mueller’s inquiry. (He has long been on the FBI’s radar, having been investigated in 2013 after an alleged Russian intelligence asset was recorded describing him as a possible target for recruitment.)

In other words, if either man was at the center of a grand scheme to share information with the Trump campaign, there’s not much sign of it in Mueller’s public actions. What’s more, neither appears to have been very close to the center of the campaign effort, having been tapped in March 2016 as part of the campaign’s effort to build a credible foreign policy advisory team.

The dossier

What we know: The Steele dossier makes a number of sweeping claims about interactions between the campaign and Russia, including that assertion about Manafort’s importance. At another point, it claims that Trump’s former attorney Michael Cohen took over management of the Russia relationship once Manafort was fired, including a report that Cohen traveled to Prague in 2016 to meet with Russian individuals.

Last year, McClatchy reported that Mueller had found that Cohen made just such a trip.

Why skepticism is warranted: That report hasn’t been corroborated and has been denied by Cohen. So far, few specific claims from the dossier have been confirmed. (Although the dossier described Page as having met with officials while in Russia in July, the identified officials don’t match with what congressional investigators determined.)

But this makes sense. If the dossier is accurate, the question of collusion has been proved ipso facto. Even less direct acts of collusion remain uncertain — as they may indefinitely.

Correction: A reference to the Times' source for its assertions about the polling has been corrected.