U.S. Senator Elizabeth Warren (D-MA) is publicly urging President Joe Biden and Lloyd Austin, Biden’s defense secretary, to take steps to limit the possible use of active-duty U.S. military and National Guard personnel against Americans once President-elect Donald Trump returns to the White House in 2025.

In a letter released Monday, Warren and U.S. Senator Richard Blumenthal (D-CT) urged Biden and Austin to issue a policy directive specifying that the federal Insurrection Act should only be used in narrow instances, e.g., when local and state authorities are overwhelmed and request assistance, or when attacks against the United States render local and state authorities incapable of effective response.

Warren and Blumenthal also suggested that the policy directive specify that presidents should consult with Congress “to the maximum extent practicable” before deploying the military under the Insurrection Act, and convey that any military domestically deployed are bound by the Standing Rules for the Use of Force “and cannot violate the writ of habeas corpus, federal law, or where applicable, federal or state law.”

As the letter notes, Trump has repeatedly spoken of using the military for domestic purposes, including securing the border and quashing protests. He also said prior to winning reelection that he would be a dictator on his first day in office but not afterward, and has described his political opponents as the “enemy within.”

Warren and Blumenthal argue that the U.S. Supreme Court’s ruling in Trump v. United States — which found that presidents enjoy broad immunity from criminal prosecution for the commission of official acts — make it especially important to limit Trump’s future use of the Insurrection Act.

“If unaddressed, any ambiguity on the lawful use of military force, coupled with President-elect Trump’s demonstrated intent to utilize the military in such dangerous and unprecedented ways, may prove to be devastating,” they wrote.

Asked if Trump could simply reverse any policy directive created by Biden, Warren told GBH News: “No policy fight is ever one and done. This action would set up a future warning alarm and force the next Trump Administration to justify any expansion of the military’s role against its fellow citizens.”

Juliette Kayyem, a senior lecturer at Harvard University’s Kennedy School of Government and former assistant secretary in President Barack Obama’s Department of Homeland Security, called the letter an attempt to convey that Trump’s possible abuse of the military poses a real and imminent danger.

“Americans seem not to believe what a threat Trump is in this regard, and I welcome putting lines in the sand,” said Kayyem, who also served as Massachusetts Governor Deval Patrick’s homeland security advisor. “It won’t have much impact on Trump, but to the extent that Democrats have a few weeks to lay the foundation to protect democracy, than this is one of the only [ways] to show how out of the norms Trump’s plans are.”