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(Former FBI Director James Comey.AP Photo/Alex Brandon)

"I've spent a lot of time studying [presidential impeachment]. We're in presidential impeachment territory," Whittington tweeted on Monday, before news of Comey's memo broke.

The memo fills in a number of details around Trump-Russia ties and what the president's motives were in firing the former FBI director, Whittington said. If Congress pursues those details, depending on what they find, this latest development may "open the door" to exploring the groundwork for presidential impeachment, he added.

And the decision over whether or not to impeach Trump over his dissemination of classified info or Comey's memo may not even come down to a question of legality.

"It may be that he's acting completely within his legal authority and yet still has abused his office in ways that might rise to the level of impeachable offenses," Whittington said. "But that would have to be something that would need to be explored through congressional hearings.

Since Watergate, many people have said that an impeachable offense is whatever the House and the Senate think it is.

Bob Deitz, a former top lawyer for the NSA and CIA, told Business Insider as much.

"I can imagine a lot of people saying, 'Look, I don't care whether what Trump did is felonious or not. But the comment itself has brought disgrace upon the White House, and therefore, we think he should be impeached for that,'" Deitz said.

And because the Supreme Court has never explicitly defined what an impeachable offense is, "since Watergate, many people have said that an impeachable offense is whatever the House and the Senate think it is," Deitz said. "It's a cynical take, but it may very well be true."

'No partisan nonsense'

An effective assessment of whether Trump has committed an impeachable offense also requires a fully-functional Congress, and that has been a source of concern among many critics who feel that officials and lawmakers may place party over country.

Preet Bharara, the former US attorney for the Southern District of New York who was fired by Trump in March, vocalized those concerns in a Washington Post op-ed titled, "Are there still public servants who will say no to the president?"

In light of Comey's abrupt dismissal while the FBI was investigating Trump's ties to Russia, Bharara argued that "we need a truly bipartisan investigation in Congress. That means no partisan nonsense — just a commitment to finding the facts, whatever they may be, proving (or disproving) Russian interference in our election and anything related."

(Majority Leader Mitch McConnell (R-KY) is flanked by fellow Republican leaders during a news conference at the Capitol in Washington on September 13, 2016.Reuters/Jonathan Ernst)

"Congress is a check and a balance," he added, "and never more important than when a bullying chief executive used to his own way seems not to remember the co-equal status of the other two branches."

And that criticism doesn't apply just to Republicans who have appeared hesitant to criticize the president. The number of Democrats who have called for Trump's impeachment since he took office doesn't help the situation either, Whittington said.

Democrats' concerns, though often outlined by lawmakers as critical to the foundation of democracy, "have not been so much about the exceptional circumstances of Trump as much as just partisan disagreements," Whittington said. And in cases where there were potential constitutional concerns — like in the case of Trump's travel ban — he has been checked by the judicial branch a number of times.

Lawmakers should be capable of stepping back and recognizing that "sometimes you just disagree and mistakes get made, but they don't necessarily rise to the level of threatening the constitutional system," Whittington said.

Instead of discussing the possibility of impeachment, Whittington said, it seems more appropriate to examine whether Trump breached his oath of office, which many experts say he did.

"I think that would be the concern," Whittington said. "I think that's the right thing to be looking at and to be thinking about," he said, adding that the focus at this point should be urging Congress to hold the president to account.

Bipartisan support for Mueller stepping in

Lawmakers from both sides of the aisle applauded the move to appoint Mueller as special counsel to oversee the Justice Department's investigation into the Trump campaign's ties to Russia, and whether his associates colluded with the Kremlin's tampering of the 2016 election.

(FBI Director Robert MuellerAP Images)

Rosenstein made the appointment after multiple revelations in the last 11 days threatened to derail the investigation.

Though Rosenstein is second-in-command at the DOJ, he has the authority to make the special-counsel appointment because Attorney General Jeff Sessions recused himself from all Russia-related investigative matters after his campaign-trail meetings with Russian Ambassador Sergey Kislyak that he failed to disclose during confirmation hearings for his role as attorney general came to light.

Experts say Mueller's appointment as special prosecutor in the Russia investigation will also ensure that it proceeds smoothly after a rocky start.

"I have enormous respect for Bob. We worked together when I was at the NSA," Deitz, who worked with Mueller when he headed the FBI, told Business Insider.

"The Russia investigation will continue apace with no loss of momentum," Deitz said. And if more evidence of Trump's or his associates' ties to Russia emerges, he said, Mueller's appointment means "the president may have gone from the frying pan into the fire."

The steady drip of new details about Trump and his associates' ties to Russia necessitated the need for a special prosecutor, Glenn Carle, a former CIA clandestine-services officer, told Business Insider. Carle called Mueller "solid," "impartial," and "professional," and also added that Mueller's appointment may temporarily stall the Russia investigation.

"Things will slow down because Mueller will be deliberate and thorough," Carle said. While he said the investigation's likely slowed pace may reduce the day-to-day tumult that has rocked the White House over the past few days, Carle added that it was likely Trump would try to "divert attention by having surrogates attack Mueller's independence and integrity."

But given Mueller's reputation as an apolitical, independent prosecutor and the precarious position the White House is currently in, Carle said, "it will be difficult for him to do so, and the costs would be high."

'Eventually the dam bursts and there is a tide'

Since the president himself has repeatedly declared that he was within his rights to take a number of actions he's taken over the last week, including Comey's ouster and repeatedly insisting that he has nothing to do with Russia, others are calling on him to back those claims up.

"If what Donald Trump says is true, that he has never done anything wrong either in the campaign or as president, he should welcome an impeachment investigation as a chance to clear the air," Allan J. Lichtman told Business Insider Germany in an interview. Lichtman has predicted every US election winner since 1984.

(Donald Trump.Pool/Getty Images)

"He should release all documents, all presidential tapes, if they exist. I would call upon him to do so. If he doesn’t do that that’s an indication he has something to hide," Lichtman added.

Lichtman also said that Republicans have been "cagey" so far.

"But it's like a dam," he said. "There's a little bit of a trickle at first, and then eventually the dam bursts and there is a tide."

The case is "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," he later added.

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

Deitz agreed and compared the current situation to the buildup to Watergate. "Republicans all lined up behind Nixon before the really damaging stuff broke," he said. "When it came out that he may have abused his power or broken the law, Republicans fled from him like rats from a ship."

"We got to wait and see whether that Republican dam is going to burst," Lichtman said.

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