In the latest sign of how perilous President Trump’s legal situation has become, several attorneys who ardently defended him in the recent past are now coming forward to raise alarms about the seriousness of the charges brought by Special Counsel Jack Smith in the federal case related to Mr. Trump’s retention of classified documents. 

Since the indictment was unsealed on Friday, high-profile attorneys who served Mr. Trump during previous Department of Justice investigations and congressional inquiries have said the indictment has the potential to send the former president away for the rest of his life. 

“I was shocked by the degree of sensitivity of these documents and how many there were,” Mr. Trump’s attorney general, William Barr, told Fox News on Sunday. “If even half of it is true, he’s toast,” he added. 

Of Mr. Trump’s claim that he is the target of a politicized prosecution, Mr. Barr said that the former president is, in fact, facing a fair process. “This idea of presenting Trump as a victim … of a witch hunt is ridiculous.” Mr. Barr also noted that he himself has defended Mr. Trump in the past when facing investigations. “Yes,  he’s been a victim in the past. Yes, his adversaries have obsessively pursued him with phony claims and I have been at his side defending against them when he is a victim. But this is much different.”

“He was totally wrong that he had the right to have those documents,” Mr. Barr said. “Those documents are among the most sensitive secrets that the country has. They have to be in the custody of the archivist. He had no right to keep them.”

A Harvard Law professor emeritus who is a longtime defender of Mr. Trump’s due process rights, Alan Dershowitz, echoed Mr. Barr’s sentiments during an appearance on Fox Business. Mr. Dershowitz, who helped lead Mr. Trump’s Senate defense during his first impeachment, said a recording in which the former president admitted to not declassifying the documents that he claimed to have declassified was a kind of smoking gun. 

“That’s a damning piece of evidence,” Mr. Dershowitz said of the recording. He did add, though, that Mr. Trump was unfairly targeted by the special counsel. 

Attorney Ty Cobb, who was part of Trump’s legal team during the Mueller investigation in the early years of his presidency, said the tape “eviscerates” the former president’s claims that he declassified information or could do so without an official order and was therefore allowed to retain the documents as a private citizen. 

“It further enhances the obstruction case because it eviscerates the two defenses that Trump has put forward,” Mr. Cobb told CNN after a transcript of the tape had been released. 

One conservative law professor who has defended Mr. Trump in the past to media outlets, Jonathan Turley, said the charges are among the most serious legal challenges the former president has faced. 

“It is an extremely damning indictment,” Mr. Turley told Fox News after the unsealing of the document. “There are indictments that are sometimes called narrative or speaking indictments. These are indictments that are really meant to make a point as to the depth of the evidence. There are some indictments that are just bare bones. This is not.”

Some of Mr. Trump’s challengers for the 2024 Republican presidential nomination are saying the charges are the most serious he has faced to date. Governor Christie, who was a member of Mr. Trump’s inner circle and once served as the United States attorney for New Jersey, told CNN that the indictment is “devastating” for the former president. “The facts that are laid out here are damning in terms of Donald Trump’s conduct,” Mr. Christie said. 

A former governor of Arkansas who is also seeking the Republican nomination, Asa Hutchinson, called on Mr. Trump to end his 2024 campaign. “With the news that Donald Trump has been indicted for the second time, our country finds itself in a position that weakens our democracy,” Mr. Hutchinson said in a statement. “This reaffirms the need for Donald Trump to respect the office and end his campaign.”

Other 2024 rivals have promised to pardon Mr. Trump should they themselves be elevated to the Oval Office. Businessmen Vivek Ramaswamy and Perry Johnson — who are polling in the single digits among primary voters — both said they would pardon Mr. Trump. 

Governor DeSantis — Mr. Trump’s most serious challenger, according to polls for the GOP nomination — has not said whether he would pardon the former president should he be convicted. He said that there should be “one standard of justice,” implying that both Secretary Clinton and Mr. Trump should be on trial for retention of classified information. 

“As a naval officer, if I would have taken classified [documents] to my apartment, I would have been court-martialed in a New York minute,” Mr. DeSantis said during a North Carolina campaign event. “Is there a different standard for a Democrat secretary of state versus a former Republican president?” 

Ahead of his arraignment at Miami on Tuesday, federal law enforcement officials are cautioning the public that there is a possibility for violence. Following the raid of Mr. Trump’s Mar-a-Lago estate in 2022, one man attacked an FBI field office in Ohio and was later killed in a shoot-out with agents.