Donald Trump. Win McNamee/Getty Images Reports that President Donald Trump asked James Comey, the former FBI director, to end the bureau's investigation into former National Security Adviser Michael Flynn has left lawmakers on both sides of the aisle shell-shocked — and openly discussing the possibility of impeachment proceedings.

Democratic Rep. Al Green on Wednesday went to the House floor and called for Trump's impeachment.

Democratic Reps. John Yarmuth and Mark Pocan have also tossed around the word in interviews, saying Democrats were "actually pretty close to considering impeachment" and that Comey's firing moved Trump's "impeachment clock" an "hour closer."

Democrats are not the only ones discussing the possibility. Republican Rep. Justin Amash told reporters on Wednesday that if the allegations contained in Comey's memo about the conversation with Trump were true, it would be "grounds for impeachment." He added that he trusted Comey more than the president, according to Katie Williams, a reporter for The Hill.

Sen. Angus King, an independent who caucuses with Democrats and sits on the Senate Intelligence Committee, told a CNN host who asked whether Congress had moved closer to the impeachment process that he would "have to say yes."

Axios reported on Wednesday that "Republicans close to the White House fear that yesterday's revelations could take President Trump into a legal or constitutional realm where his staff and supporters can't save him." A Republican operative told the publication that "a whole new door has opened" that could move the administration "backwards" instead of "the agenda grinding to a halt."

Trump and James Comey, the former FBI director. Thomson Reuters

At an award dinner on Tuesday night, Republican Sen. John McCain told reporter Bob Schieffer that the Trump scandals had reached a "Watergate size and scale."

"I think we've seen this movie before," McCain said. "The shoes continue to drop, and every couple days there's a new aspect."

The famously hawkish senator did not mention the word impeachment. But he drew further comparisons to President Richard Nixon, telling Schieffer that he would advise Trump to do "the same thing" Nixon was advised to do before he was faced with impeachment proceedings: "get it all out."

"It's not going to be over until every aspect of it is thoroughly examined and the American people make a judgment," McCain said. "And the longer you delay, the longer it's going to last."

In the UK, betting odds imply a 55% chance Trump will not last four years in office, according to Katie Baylis, a spokeswoman for the British betting firm Betfair.

"And many punters think it won't be too long before he departs," Baylis added, "with the odds of him leaving this year now into 12-5 from 11-2 — a 27% chance [up] from 16% before the latest allegations."

'Drip, drip, drip'

Allan Lichtman, a political historian and American University professor, said the case was "becoming too compelling for even Republicans to resist an impeachment inquiry," which they may be tempted to use "to get to the bottom of the many controversies swirling around this administration."

"Otherwise, it's going to be drip, drip, drip, which is not good even for Republicans," Lichtman said.

The latest Trump-Comey bombshell came one day after the previous one — that Trump disclosed highly classified information to Russian Foreign Minister Sergey Lavrov and Ambassador Sergey Kislyak during a meeting in the Oval Office last week.

It also came less than a week after the Trump administration wavered in its public statements about Comey's dismissal. Trump told NBC News' Lester Holt that "the Russia thing" was on his mind when he fired Comey, which contradicted earlier statements from his aides, who claimed Trump fired Comey on the recommendation of Deputy Attorney General Rod Rosenstein.

Deputy Attorney General Rod Rosenstein. AP Photo/Patrick Semansky

Noah Feldman, a professor at Harvard Law School specializing in constitutional studies, predicted that Republicans would first "gauge public reaction" to the Comey reports before launching impeachment proceedings.

"But we are gradually moving in that direction," Feldman said.

Louis Seidman, a professor of constitutional law at Georgetown University, said that "the right question is not legal, it is political: Has the president violated the oath he took to support and defend the Constitution of the United States? Lawyers and law professors have no special expertise about that. It's an issue for the American people to decide."

Seidman said he remained skeptical, however, that impeachment was a serious possibility.

"It seems to me quite unlikely, at least at this point, that Trump will face impeachment proceedings," he said. "Most Republicans seem to have cast their lot with President Trump."

Hugh Gusterson, an anthropologist at George Washington University, said in an email that, "by coincidence," he spent most of Tuesday "talking to various staffers and one senator on the Hill."

"No one raised the issue of impeachment. They all seemed to assume they would have to muddle on through the chaos. But everyone I spoke to was a Democrat, and when I asked them what Republicans were thinking, they didn't seem to know," Gusterson said. "On the other hand, reading conservative commentators in [Tuesday's] Washington Post, I thought I detected a shift in tone."

House Speaker Paul Ryan. Win McNamee/Getty Images

Veteran political operatives David Axelrod and David Gergen predicted the Comey memo could spur House Republicans to consider impeachment proceedings.

"I've been resistant to impeachment talk until now, but if Comey memo is true — and Comey is very credible — we are into a whole new deal here," Axelrod, who advised President Barack Obama, tweeted on Tuesday night.

Gergen, who advised Presidents Ronald Reagan, Gerald Ford, Richard Nixon, and Bill Clinton, told CNN on Tuesday night that Trump was now "in impeachment territory."

"It looks like he was trying to impede the investigation," Gergen said. "He was using his power to do that, and when James Comey didn't go along with him, when he wasn't his boy, he fired him."

He added: "After watching the Clinton impeachment, I thought I'd never see another one. But I think we're in impeachment territory now for the first time."

Seidman said it was worth emphasizing that "there are all sorts of considerations that members of the House might appropriately consider, but that would be improper for a judge or jury to take into account."

"For example," he said, "what the effect would be of removing a president when something like a third of the country would believe that their election victory was stolen from them, how much risk there is that this president's poor judgment will lead to truly catastrophic consequences for the country, and whether the vice president would do a better job."

Democratic Rep. Adam Schiff, the ranking member of the House Intelligence Committee, seemed to echo those concerns in an interview with CNN on Wednesday morning.

He said there was "no avoiding having to answer the question" of whether impeachment was a possibility.

"But I do think that all of us ought to talk about just what a wrenching experience that would be for the country," Schiff said. "That's not something that we should be rushing into or rushing to suggest.

"We need to get to the bottom of what took place," he added. "What was the president's intention was in doing this? Was he trying to shut down a legitimate prosecution? Was he doing it because ultimately he was worried the trail might ultimately lead back to him? These are some profound questions I think we need to answer before we get too far down the path of what are the consequences if the proof turns out to be there?"