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

At District of Columbia Mayor Muriel Bowser's request, Army Secretary Ryan McCarthy has activated about 340 unarmed D.C. National Guardsmen to assist local law enforcement with the demonstrations taking place on Wednesday pegged to the Electoral College certification.

"We think it's helpful to have our D.C. Guardsmen, who are our Guard, that I have requested from the Secretary of the Army to assist MPD [Metropolitan Police Department] with traffic management," Bowser said Monday. "It absolutely frees up more officers."

The D.C. Guard is unique in that any call-ups have to be made by the Army secretary and not the jurisdiction’s top elected official -- as is the case with state governors. Additionally, more focus has been given to the call-ups since the controversial presence of D.C. Guardsmen and the use of D.C. Guard helicopters during the Black Lives Matter demonstrations last summer.

"They will be deployed to assist us with crowd management, as well as traffic control in our nation's capital that will allow for the police officers to focus on anyone who's intent on instigating agitating or participating in violence in our city," said D.C. Police Chief Robert Contee. He also labeled any possibility of violence surrounding the protests as "unacceptable" and repeated that carrying firearms is not allowed under D.C. law.

A senior defense official said Bowser put in the request for Guardsmen on Dec. 31 and that it was approved Monday morning. Beginning Tuesday through Thursday, the 340 personnel will help man 30 traffic control checkpoints around the northern side of the downtown area close to the National Mall.

"No one's going to be armed or body armor or anything like that," said the official. "What they need is traffic control."

-ABC News' Luis Martinez and Quinn Owen