Senate Democrats issued stark warnings on Wednesday that Republicans would severely damage the institution of Congress if they acquiesced to a push from Trump allies to haul former Vice President Joe Biden and his son Hunter for testimony about their actions in Ukraine.

A top Biden ally, Sen. Chris Coons (D-DE), told The Daily Beast that calling the 2020 presidential contender—who served for 35 years in the Senate—and his son for testimony “would be literally rolling a grenade down the aisle of the Senate” that would have “lasting consequences” on the upper chamber’s ability to work together.

"Look, Joe Biden is well known, widely respected, and frankly beloved by many in the Senate on both sides of the aisle,” said Coons. “The impeachment process is already disruptive enough. I think we should be approaching it with seriousness, not by entertaining conspiracy theories that are utterly unfounded. And I think it would be a very unfortunate move."

The idea of bringing in the Bidens to testify has gained traction in recent days as allies of President Donald Trump have flirted with counter-programming the impeachment proceedings in the House by having the GOP-led Senate call witnesses of their own.

Last month, Sen. Lindsey Graham (R-S.C.), who chairs the Judiciary Committee, expressed interest in calling the Bidens for testimony. And this week, Sen. Rand Paul (R-KY) stood on a rally stage alongside President Trump in Kentucky and urged the Senate to call not only the anonymous whistleblower for testimony, but the Bidens, too.

“The Republicans must call the Bidens to the hearings to answer to the nation about their corruption,” the president’s former strategist, Steve Bannon, told The Daily Beast. “In addition, it’s incumbent upon [Sen. Elizabeth] Warren and [Sen. Bernie] Sanders not to repeat '16 and Clinton—but to call out the permanent political class."

But top Republican leaders in the Senate have so far resisted going down that route. Senate Foreign Relations Committee chairman Sen. Jim Risch (R-ID), whom Graham has since deferred to on the issue of hearings, has suggested that his committee would stay away the Bidens, for now.

“I believe it would be more appropriate to wait on examining these matters until after the House completes its process (one way or another),” Risch wrote in an Oct. 29 letter to the committee’s ranking member, Sen. Robert Menendez (D-N.J.). “It is important that the Senate reserve judgment on these matters until the House formally completes its work on this inquiry.”

And even many rank-and-file members have been skeptical of the idea of hauling in the Bidens, saying that they need to keep distance from such matters as potential jurors in the case of a potential impeachment trial. Sen. Ron Johnson (R-WI), who chairs the Senate’s panel on oversight and could call certain witnesses if he wanted, said he’d be interested in hearing from the Bidens “at some point in time” but indicated he was not interested in “show trials.” The senator, who has found himself as a side player in the Trump-Ukraine saga, has frequently referenced reporting from John Solomon, the conservative reporter whose work, while criticized on the merits, has fueled allegations of corruption against the Bidens.

“I'm just trying to tenaciously gather information so we can, at some point in time, determine the truth,” Johnson told reporters on Wednesday.

Though senators from both parties appear hardly eager to jump into the impeachment debate, news of the push for the Bidens to be called to testify, which was first reported by The Washington Post, did prompt admonishments from Democrats, who argued that it would be a step too far for a chamber that still values decorum even if it remains irregularly practiced.

Some Senate veterans said that they were looking back to the impeachment of Bill Clinton—a moment marked by partisan rancor unprecedented at the time—as an example for how both parties could navigate the tricky waters ahead.

Sen. Dick Durbin (D-IL), who served alongside Biden and was in office for Clinton’s impeachment, recalled that saga as being bitterly fought, but ultimately one that didn’t ruin the chamber.

“We should really accept our responsibility to be dignified, independent, and thoughtful in the way we handle it,” Durbin said. “It’s much worse than it was 20 years ago, but I still have faith in my colleagues on both sides, that they understand that we have a historic responsibility here.”

Durbin also dismissed the idea of the Bidens appearing for testimony, calling it a political stunt. “The next thing we can expect them to do is to say, Hillary Clinton has to testify,” he said.

Biden himself has steadfastly stated that both he and his son did nothing wrong. He has noted that he never actually talked to his son about official business involving Burisma, a Ukrainian natural gas company on whose board the younger Biden served. And he has stressed that his calls for the ouster of Ukraine’s prosecutor, Viktor Shokin, had to do with the fact that Shokin wasn’t prosecuting corruption and not—as critics contend—that he was investigating Burisma.

Those facts have done little to persuade elected Republicans, who have either avoided coming to Biden’s defense or echoed the president in insisting that something untoward took place. But on Wednesday, Biden was in D.C. for a campaign fundraiser, during which he insisted, once more, that Republicans would self-moderate once Trump was gone from office.

“With Donald Trump out of the way, you’re going to see a number of my Republican colleagues have an epiphany,” Biden said on Wednesday at a fundraiser in Washington, not far from the building where Republicans had spent the last month sliming him as corrupt. “Mark my words. Mark my words.”