Democrats plumb election timeline for Trump-Russia clues

— -- As the number of documented contacts between Trump campaign aides and Russian officials grows, congressional investigators are increasingly looking at the events that occurred around those meetings to determine if they provide evidence of a Russian influence campaign.

“Whether there was any collusion there is of keen interest to our committee,” said Rep. Adam Schiff (D-CA), the ranking Democrat on the House Intelligence Committee. “This could all be coincidence or could be collusion.”

Trump has continually denied lingering allegations that associates of his campaign had been in contact with the Russians. In a Feb. 16 news conference, Trump underlined previous denials, saying, "I have nothing to do with Russia. I told you, I have no deals there, I have no anything," and said that "the news is fake."

Senior Republican leaders in Washington have said they remain unconvinced the timeline points to anything out of the ordinary.

“We have seen no evidence from any of these ongoing investigations that anybody in the trump campaign or the trump team was involved in any of this,” House Speaker Paul Ryan (R-WI) told ABC News’s Mary Bruce. “We've been presented with no evidence that an American was colluding with the Russians to meddle in the election.”

A key period that is gaining interest from investigators is July 2016, as the Republican National Convention got underway in Cleveland. On July 18, party insiders took the unusual step of altering the official GOP platform by watering down its position on the use of force to protect the Ukraine from Russian incursions.

“The champagne corks were going off when that happened,” said Paul Joyal, a Russian intelligence expert and managing director of National Strategies.

Two days later, on July 20, the Russian Ambassador to the United States surfaced in Cleveland, meeting at different points with then-Senator Sessions (R-AL) – who served as a campaign advisor and now as Trump's Attorney General – and with a one-time Trump foreign policy adviser named Carter Page. Page later denied any meeting had occurred, telling PBS Newshour, “I had no meetings. No meetings.”

That same week, on July 22, WikiLeaks posted the first of the hacked Democratic party e-mails.

“July seems to be a key month,” Schiff told ABC News.

Sen. Mark Warner (D-VA) told ABC News he considered that month to be a turning point. He said investigators are likely to explore how hackers changed their approach to releasing stolen material.

“The selective leaking of that information in a way that was I think initially just to throw chaos into the election but increasingly about mid-summer switched from let's just throw chaos into let's favor Mr. Trump – at the expense of Hillary Clinton,” Warner told ABC News.

He specifically noted the timing of leaks revealing Clinton campaign chairman John Podesta’s emails. The first of those leaks occurred just hours after Trump had suffered a public relations blow from the release of embarrassing hot mic recordings of Trump on the Access Hollywood entertainment program in 2005.

“That was more than coincidence,” Warner said.

Schiff cautioned that it remains far too soon to draw any conclusions.

“I see as my responsibility is to follow the facts wherever they lead,” Schiff said.

ABC News' Cho Park, Alex Hosenball and Paul Blake contributed to this report.