(CNN) The charges against three former Trump campaign aides this week provided a jolt to congressional Russia investigators who now know special counsel Robert Mueller is moving quickly — and his moves will shut down potential lanes of inquiry for them and likely eliminate the chances of lawmakers to question those aides.

Mueller's investigation, which has already led to some dust-ups with the Hill , threatens to limit the scope of the congressional Russia probes even further. And Democrats are increasingly coming around to the idea that Mueller may be their best shot at proving whether there was collusion between the Trump campaign and the Russians — given the reticence of most Republicans to break ranks from the White House and embrace the notion of Trump-Russia ties.

Take President Donald Trump's former campaign chairman Paul Manafort. The Senate intelligence committee had interviewed him about the June 2016 meeting with Russians and Donald Trump Jr. but still hoped to speak to him again about a broader range of issues, while the House intelligence panel had still yet to schedule an interview. The Senate judiciary committee was also seriously weighing a subpoena for his testimony.

Now that's almost assuredly a non-starter.

"He's under federal indictment. He won't come, his lawyer won't let him come. And if he comes he'll take the Fifth," said California Sen. Dianne Feinstein, the top Democrat on the Senate judiciary committee who has been pressing for Manafort's appearance since the summer. "And you know what, what you do is you see the importance of a Mueller investigation, because if you think about it, we have the power of subpoena and not telling a lie to the Congress — that's it."

But Manafort is not the only roadblock. The House intelligence committee had planned to speak this fall with Rick Gates , the Manafort business associate and former Trump aide who was also indicated Monday. Sources said familiar with the matter said that it was delayed as Gates continued to reschedule his appearance, and now it's possible that it never occurs.

Senate Intelligence Chairman Richard Burr said that the Trump foreign policy adviser George Papadopoulos -- who pleaded guilty to lying to federal investigators about his efforts to arrange high-level Russian meetings with Trump officials -- had been in "constant contact" with the committee through his lawyer.

Asked Tuesday if that discussion is over, the North Carolina Republican said: "I think it is."

The gap between Republicans and Democrats on whether there is evidence of collusion between the Trump campaign and Russia is only growing in the wake of Mueller's charges.

If Congress cannot interview key figures, it could make it harder to reach definitive conclusions on a bipartisan basis in reports designed to tell the public the extent of the Russian meddling in the last elections.

The gap between Republicans and Democrats on whether there is evidence of collusion between the Trump campaign and Russia is only growing in the wake of Mueller's charges.

To Democrats, Monday's indictment of Trump's former campaign chairman and the guilty plea of a foreign policy adviser who was offered "dirt" from the Russians on then-Democratic presidential candidate Hillary Clinton shows evidence of at least an intent to collude, and the developments provide the congressional probes new avenues to explore.

"There are clearly facts and evidence that show collusion by the Trump campaign with the Russians, at least individuals involved in the Trump campaign," said Sen. Richard Blumenthal, a Connecticut Democrat. "We are nowhere near the end of this investigation. There is a lot more to be known."

The new revelations -- particularly over Papadopoulos and the offer of Clinton dirt -- added fuel to their push to prove that the Trump campaign had wittingly or unwittingly been used by Russian operatives to meddle in the elections.

"This is a wake-up call," said Rep. Eric Swalwell, a California Democrat on the House intelligence committee. "We have more clear evidence than ever that people at all levels of the campaign sought to work with the Russians. Now we have someone who put his name on a piece of paper under penalty of perjury and said he did that."

But Republicans are not moved. Top Republicans on the committees probing Russian election meddling say this week's developments do not change their investigation, nor do they add up to collusion.

"I'm not sure that it changes anything for our investigation," Burr said. "I don't think the indictments were a surprise to any of us who had been involved in the investigation for nine months."

"It looks to me like it's disconnected from what we're looking at," said Sen. Jim Risch of Idaho, another senior Republican on the intelligence panel.

In the aftermath of Mueller's charges, some lawmakers remain hopeful that they will have access to some of the officials tied up in the special counsel investigation.

Rep. Adam Schiff, the top Democrat on the House intelligence committee, expressed optimism that Papadopoulos would be willing to talk to the panel now that he's cooperating with Mueller's probe.

"I would hope that as part of his plea agreement, his cooperation will extend to the congressional probes as well as to investigators," Schiff said. "In the near term, I would imagine Manafort and Gates who were also on our witness list would be less likely to testify."

Sen. Mark Warner, the top Democrat on the Senate intelligence panel, said "there are more questions that need to be answered" in the aftermath of the Mueller moves.

"We continue to see evidence that Russians were reaching out to Trump officials in a variety of ways, offering discrediting information on Hillary Clinton that included their email," Warner told CNN.

Before Mueller's charges were revealed this week, there have already been growing calls from Republicans to wrap up the Hill probes this year, with accusations that Democrats are trying to drag out the probes into the 2018 election cycle.

While Burr said Tuesday the panel had not come to a conclusion on collusion, he downplayed the significance of the new revelations in the court documents.

"If indictments were all about Russians reaching out to Americans, it would be a lot of people who would have been indicted yesterday," Burr said. "So we know from this investigation that there's been an active campaign by the Russians to be involved in the 2016 election on both sides and we're going to try to answer some of the questions."

Sen. Susan Collins, a moderate Republican who sits on the Senate intelligence committee, said she still has not seen "definitive evidence of collusion."

"I have read the (Papadopoulos) plea agreement and I think it raises questions but ... based on the information that I've reviewed through the intelligence committee investigation that I have yet to see any definitive evidence of collusion," Collins said.

And she added that it could be Mueller who ultimately answers that question.

"One reason we have a special counsel to pursue any evidence of criminal wrongdoing is to help us get to the answer of that question," Collins said. "Obviously the intelligence committee is unable to bring criminal charges, which gives a certain leverage in dealing with individuals that you might not otherwise have."