The Senate Intelligence Committee is approaching a major decision point in its investigation into Russia's election interference where lawmakers will weigh in on whether members of President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s campaign colluded with Moscow.

The question risks dividing a panel that has kept a bipartisan facade for nearly two years since the committee began its investigation. The final conclusion is sure to be a major flashpoint in a probe that has largely prodded along behind the scenes, as lawmakers and committee staff interview witnesses and prepare reports on their findings.

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The notion of potential collusion has produced fractures in Washington that have only deepened as special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE has pressed forward with his Russia investigation, which runs parallel to the congressional probes.

The president’s critics have seized on revelations about the June 2016 Trump Tower meeting and longtime Trump associate Roger Stone Roger Jason StoneThe agony of justice Our Constitution is under attack by Attorney General William Barr Justice IG investigating Stone sentencing: report MORE’s links to WikiLeaks as indicators of collusion, while Trump’s defenders have accused the FBI of exhibiting bias in its decision to open the federal investigation into Russian interference.

Senate Intelligence Committee leaders Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R-N.C.) and Mark Warner Mark Robert WarnerDemocrats call for declassifying election threats after briefing by Trump officials It's time to upgrade benefits Intelligence chief says Congress will get some in-person election security briefings MORE (D-Va.) have gone to great lengths to keep their investigation bipartisan amid the rancor, in contrast to the now-defunct probe in the House.

Lawmakers have seemed to break along party lines when talking about evidence of collusion, though they have chosen their words carefully. Burr has said repeatedly that he’s seen no definitive evidence of collusion, but he has also not ruled out that it could arise as the investigation continues.

“I can say as it relates to the Senate Intelligence Committee investigation, that we have no hard evidence of collusion,” Burr told Fox News in September. “Now, we’re not over, and that leaves the opportunity that we might find something that we don’t have today.”

Trump seized on that quote as recently as Thursday, telling Fox News that it vindicates his claims that there was “no collusion.”

Sen. James Lankford James Paul LankfordMcConnell works to lock down GOP votes for coronavirus bill Charities scramble to plug revenue holes during pandemic Warren calls for Postal Service board members to fire DeJoy or resign MORE (R-Okla.) told The Hill Thursday he has seen no evidence of collusion, and that he hoped the question would not divide Republicans and Democrats on the panel as they seek to produce a report.

“I really hope it doesn’t,” Lankford said. “It shouldn’t, because we’re all looking at the same facts.”

Warner has said he will reserve his final judgment after all witnesses are interviewed on the collusion angle. Other Democrats have gone further; Sen. Ron Wyden Ronald (Ron) Lee WydenDemocrats call for declassifying election threats after briefing by Trump officials Read Democrats' report countering Republicans' Biden investigation Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy MORE (D-Ore.) has said that Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE’s communications about the June 2016 Trump Tower meeting show “an intent to collude.” Still, none have publicly claimed to have seen evidence of collusion.

Sen. Angus King Angus KingGovernment watchdog recommends creation of White House cyber director position Democrats step up hardball tactics as Supreme Court fight heats up Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' MORE (Maine), the committee’s only independent member, on Thursday declined to comment on whether he had seen evidence of collusion but called that judgment the “hard part” of the investigation.

“I’m hoping we can finish by the end of the year,” said King, an independent who caucuses with Democrats. “We’ve pretty much completed the work on the social media part, and then after that is the hard part — the collusion issue. And we’re working on it. We’re interviewing witnesses, so we’re at it.”

The investigation could ultimately fall victim to partisan divides, especially as Trump grows increasingly critical of the Mueller investigation.

A committee aide stressed that the goal from the start has been to issue one bipartisan report on the investigation’s findings.

“The goal and operating assumption is that there will be one bipartisan report,” the committee aide said. “The committee’s investigation is fact-based and that has been the agreement from the chair and vice chair since the beginning.

It is also possible, but appears less likely, that Republicans and Democrats could ultimately issue two different reports on their findings.

The House Intelligence Committee’s investigation infamously plunged into partisan infighting, resulting in Republicans unilaterally voting to end it in March and releasing a report that found no evidence that the campaign colluded, coordinated, or conspired with the Russian government. Democrats accused their GOP colleagues of shuttering the probe prematurely and pointed to what they called ample evidence of collusion.

The investigation in the upper chamber has been markedly different, enjoying comparatively little media attention as a result of how little members have said publicly about the probe.

“What we’ve seen, and the House side is a perfect example, is when they’re not working in tandem, you generally see indications of it,” observed Steven Cash, a lawyer at Day Pitney and former Senate Intelligence Committee staff member. “If you’re looking for a bipartisan investigation, silence is golden, from the outside perspective.”

The Senate panel upheld the intelligence community’s assessment that Russia interfered in the election to help Trump win, in a dramatic break with its House counterpart earlier this year. The committee has also released a report on election security, finding that Moscow conducted an “unprecedented, coordinated cyber campaign” against U.S. voting infrastructure.

The committee members are completing reports on Russia’s use of social media and the Obama administration’s response to the meddling effort and continuing to interview witnesses, before moving to a judgment on collusion. Last week, Randy Credico, an associate of Stone, pleaded the Fifth to avoid testifying. The committee has reached out to WikiLeaks founder Julian Assange for an interview. Lawmakers have also signaled they want to bring Michael Cohen, Trump’s former personal attorney, back for questioning.

Democrats have been pressing for future open hearings, but there have been no agreements reached.

Lawmakers say they hope to wrap up the investigation by the end of the year, though Burr and Warner have offered no definitive timeline on its completion. Burr said Thursday that the committee would go “dark” until after the November midterm elections, a decision that reflects lawmakers’ recognition of the sensitivity of the probe.

It’s possible that the results of the midterms could change the landscape dramatically, putting Democrats in charge of the House and allowing them to revive the lower chamber’s Russia investigation. There is also the less likely prospect of Democrats retaking the Senate.

“We’ve gone dark until after the election,” Burr told The Hill Thursday.

“I think that we have a goal, but we have some people to work through,” Burr said when asked for a timeline. “As soon as we get through the election, we’ll give everybody an update.”