WASHINGTON — An attorney for Democratic Sen. Elissa Slotkin is warning Attorney General Todd Blanche not to bow to President Donald Trump’s demand for a criminal investigation into her political speech.

Over the weekend, Trump posted on his social media platform that he was demanding the Justice Department look into the Michigan senator’s recent comments about how Democratic investigations into the Trump administration could send a “deterrence message” to young people thinking about joining the administration in its final two years.

“By copy of this statement, I am ordering the Department of Justice to look into this criminal act, immediately!” Trump wrote.

In a letter to Blanche made public Monday, Preet Bharara, the former U.S. attorney in the Southern District of New York, wrote that it “should not be hard to make clear that we do not live in an authoritarian regime where mere criticism of the powerful can land anyone in legal peril and possibly prison.”

“That requires a clear and public statement confirming that the Department will not pursue this investigation against Senator Slotkin,” he wrote.

The Justice Department didn’t comment on Trump’s post.

The attorney general is appointed by the president and is a member of his Cabinet, but it’s still highly unusual for the White House to publicly demand an investigation. The Justice Department has long sought to separate politics from the law. But under Blanche, Trump’s former personal attorney, the department has investigated many of the president’s perceived political enemies.

Slotkin, a former CIA and Defense Department official, was also one of a group of lawmakers the Trump administration tried and failed to indict earlier this year over a social media video.

A few weeks before the midterm elections, where the GOP saw massive losses, she spoke at the University of Chicago, arguing that Democrats should focus investigative efforts on those who enable Trump. She said she hoped to deter young people coming out of school from joining the administration.

“I want them to be like, ‘Lord, that might be buying myself a ton of problems that I don’t want, and so let me avoid participating in that,’” Slotkin said. “I want that deterrence message sent.”

In his post on Truth Social over the weekend, Trump accused Slotkin of “going to go after all young people that believe in Republican Values, and that give even the slightest inclination to be a Republican.”

Trump’s demand came weeks after Trump ally Mike Davis requested that Harmeet Dhillon — who has since resigned as head of the Civil Rights Division — launch an investigation of Slotkin.

Bharara wrote that Slotkin’s comments were “entirely lawful” and protected by the First Amendment as well as the “speech and debate” clause of the Constitution, which protects members of Congress.

“There is no conceivable basis to investigate the Senator for reminding members of the executive branch who aid the President’s law breaking that there will be accountability for their actions, or expressing the hope that Americans decline to serve in an administration where leaders may ask them to violate the law or misuse taxpayer dollars,” Bharara wrote. “Indeed, the Senator’s statement reinforces the rule of law.”

Bharara asked Blanche to publicly decline to follow Trump’s command.

“The Department should stop threatening our constitutional freedoms and make clear that you will not again launch another frivolous investigation at the taxpayers’ expense,” he wrote.

The Justice Department did not immediately respond to a request for comment.

Bharara’s letter noted that it had been less than a year since the administration failed to indict Slotkin and five other members of Congress over a social media video that reminded members of the military and intelligence communities of their duties not to follow unlawful orders.

“Thankfully, the anonymous citizens of a Washington D.C. grand jury unanimously rejected the Department’s attempt to punish a perceived political adversary for her lawful — indeed, constitutionally privileged — speech,” Bharara wrote.