The indictments of a former director of the FBI, James Comey, and New York’s attorney general, Letitia James, could set the stage for the Trump administration to pursue a sitting United States senator — California’s Adam Schiff.

Mr. Trump took to Truth Social on Sunday to declare, “The Ukraine Impeachment (of me!) Scam was a far bigger Illegal Hoax than Watergate. I sincerely hope the necessary authorities, including CONGRESS, are looking into this! Adam ‘Schiffty’ Schiff was sooo dishonest and corrupt. So many laws, and protocols, were violated, and just plain broken!!!”

Mr. Schiff, who led the first impeachment of Mr. Trump, is under criminal investigation by the Department of Justice for allegations of mortgage fraud. Those accusations were first surfaced by the director of the Federal Housing Finance Agency, William Pulte — himself the heir to a home construction fortune. Mr. Pulte alleges that Mr. Schiff listed both a Potomac home and a Burbank one as his primary residence in order to secure lower mortgage rates.

The senator has proclaimed his innocence, declaring in a video message, “This is the kind of stuff you see tinpot dictators do. It is designed to intimidate his political opponents and somehow try to silence them.” Mr. Schiff’s high-profile lawyer, Preet Bharara, calls the accusations “transparently false, stale, and long debunked.” The government, though, reckons that Mr. Schiff engaged in a “sustained pattern of possible occupancy misrepresentation.”

A spokesman for Mr. Schiff explains that the lawmaker “received the rate that each lender deemed appropriate with full knowledge of the senator’s year-round bicoastal work obligations as a member of Congress, his use of two homes for that reason, and his creditworthiness.” A special attorney for mortgage fraud, Ed Martin, has been appointed to coordinate the investigations into Ms. James and Mr. Schiff. A grand jury in Maryland is weighing whether to indict the Californian.

The Old Line State is also the home of a former national security advisor, John Bolton, who is under investigation for his handling of classified materials and potentially leaking some of them to the press. Mr. Bolton, who was also America’s ambassador to the United Nations, could be charged with violations of the Espionage Act. Special Counsel Jack Smith charged Mr. Trump with violating that statute in connection with the storage of records at Mar-a-Lago.   

Mr. Trump, though, appears to be floating a fresh theory for criminality that stems from his impeachment in 2020 on accusations of abuse of power and obstruction of Congress. He was acquitted by a vote of the Senate. Mr. Schiff and House Democrats alleged that Mr. Trump withheld $391 million in aid and an invitation to the White House from President Volodymyr Zelensky of Ukraine in order to prod Ukraine to investigate the Biden family.

Last month, Mr Trump wrote in a Truth Social post addressed to “Pam” — Attorney General Pam Bondi — that “Nothing is being done. What about Comey, Adam ‘Shifty’ Schiff, Leticia???” The Wall Street Journal reports that the missive was intended to be a direct message to America’s top law enforcement official. Now Mr. Schiff is the only one of that trio who has not been charged.

While it is not immediately clear how Mr. Schiff could be charged for his starring role in the impeachment saga, the Republican-controlled Congress could make life difficult for him. When the shoe was on the other foot and Democrats controlled the legislature and the Department of Justice, an adviser to Mr. Trump, Stephen Bannon, was referred by the lawmakers for criminal contempt of Congress for refusing to appear before the January 6 committee.

Mr. Bannon was eventually convicted on two charges and served four months in prison. Last week the host of the “War Room” podcast asked the Supreme Court to review that conviction on technical grounds. Another adviser to Mr. Trump, Peter Navarro, was also convicted of contempt of Congress and served the same four-month sentence as Mr. Bannon.

Mr. Schiff is likely to challenge any attempt to prosecute him for his work as a solon by citing the Constitution’s “Speech or Debate” clause, which ordains that lawmakers “shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their Attendance at the Session of their respective Houses, and in going to and returning from the same; and for any Speech or Debate in either House.”

The protection is an absolute bar to prosecution that applies when legislators are “acting in the sphere of legitimate legislative activity.” The Supreme Court has held that in such cases law makers are “protected not only from the consequence of litigation’s results but also from the burden of defending themselves.”