Another prominent former Republican leader has broken his silence on Trump and the Republican Party Thursday, with former House Speaker John Boehner calling for the GOP to "awaken" following Wednesday's "invasion" of the U.S. Capitol.

"I once said the party of Lincoln and Reagan is off taking a nap. The nap has become a nightmare for our nation. The GOP must awaken. The invasion of our Capitol by a mob, incited by lies from some entrusted with power, is a disgrace to all who sacrificed to build our Republic," Boehner said in a tweet.

Rep. Adam Kinzinger, R-Ill., now one of Trump's fiercest critics on Capitol Hill, is the first Republican to publicly call for the invocation of the 25th Amendment to remove him from office.

"Sadly, yesterday it became clear that the president not only abdicated his duty to protect the American people and the people's house, he invoked and inflamed passions that gave fuel to the insurrection we saw here," Kinzinger said in a video posted to Twitter. "When pressed to move and denounce the violence he barely did so, while, of course, victimizing himself."

"All indications are that the president has become unmoored, not just from his duty, or even his health, but from reality itself. It is for this reason that I call for the vice president and members of the Cabinet to ensure that the next few weeks are safe for the American people, and that we have a sane captain of the ship," he added.

Kinzinger also spoke forcefully against the Electoral College challenge -- and his colleagues' support of it -- during the House debate Wednesday night over the ratification of Pennsylvania's vote.

-ABC News' Benjamin Siegel

White House Deputy National Security Adviser Matthew Pottinger resigned on Wednesday, according to a White House official and a person familiar with his resignation, joining a slate of White House staff to resign in the wake of Wednesday's rioting at the U.S. Capitol.

The White House’s National Security Council did not respond to questions about Pottinger, who was an assistant to the president.

-ABC News' Chief White House Correspondent Jonathan Karl and Ben Gittleson

Former Attorney General Bill Barr, once one of President Trump's most loyal allies, is speaking out against his former boss in light of Wednesday's storming of the U.S. Capitol, saying in a statement that his conduct "was a betrayal of his office and supporters."

“Orchestrating a mob to pressure Congress is inexcusable. The President’s conduct yesterday was a betrayal of his office and supporters," he said in a statement to the Associated Press, which was obtained by ABC News.

Barr resigned last month with five weeks remaining in Trump's term after months of growing tensions with Trump that culminated in Barr's refusal to announce investigations into Trump's political opponents and his public rebuke of Trump's baseless claims of widespread voter fraud in the 2020 election.

-ABC News' Alexander Mallin

Georgia election official Gabriel Sterling, a Republican, at a press conference on what he called "anti-disinformation Monday," ran through major voter conspiracies pushed by Trump, his allies and far-right media outlets and debunked them one-by-one in an effort to restore faith in Georgia's election system.

"The reason I'm having to stand here today is because there are people in positions of authority and respect who have said their vote didn't count and it's not true," Sterling said, stressing to Georgians that their votes count ahead of critical runoffs in the state which will determine the balance of power in the U.S. Senate.

"It's Whac-A-Mole again. It is Groundhog Day again. I'm going to talk about the things I've talked about repeatedly for two months, but I'm going to do it for one last time," Sterling said, adding he "screamed" at the radio upon hearing audio of the phone call between Trump and Secretary of State Brad Raffensperger because theories Trump questioned have already been "thoroughly debunked."

For example, Sterling, responding to those who claim there were roughly 2,500 people who voted without being registered, said, "Let's just be clear about this: you can't do it!" He said, "So that number is zero," going on to debunk other theories.

Asked if he believes, as some have said, that Trump's phone call was an attack on democracy, Sterling said he'd leave others to make that decision before adding he felt it was "out of place."

"I found it to be something that was not normal -- out of place -- and nobody I know who would be president would do something like that to a secretary of state," Sterling said.

Asked about Raffenperger's desire to have the phone call recorded and whether he was concerned about anything improper being said or needing to release it later, Sterling said it was recorded "out of an abundance of caution"

"I think given the environment we're in right now, the political situation that we're in, the history of the president, knowing that he sometimes doesn't necessarily characterize things as they might have actually occurred, it was out of abundance of caution," Sterling said.

"I'm sure the president's side may have recorded it, too. They may have been the ones who leaked part of that, too," he added.