The group of Democratic senators and representatives, who all have military or intelligence service backgrounds, made the comments in a video posted Tuesday on X.

They did not specify which orders they were referring to, but Trump's administration has come under fire for its employment of US forces both at home and abroad.

"This is really bad, and Dangerous to our Country. Their words cannot be allowed to stand. SEDITIOUS BEHAVIOR FROM TRAITORS!!! LOCK THEM UP???," Trump said on Truth Social.

He then added in a later post: "SEDITIOUS BEHAVIOR, punishable by DEATH!"

Trump also reposted a message from a user urging him to "hang them" and saying that the first US president, George Washington, would have done the same.

The lawmakers behind the message included Senator Mark Kelly, a former member of the Navy and NASA astronaut, and Senator Elissa Slotkin, who served with the CIA in Iraq.

The six accused the Trump administration of "pitting our uniformed military and intelligence community professionals against American citizens."

"Right now, the threats to our constitution aren't just coming from abroad, but from right here at home," they said, adding: "You can refuse illegal orders."

- 'Not partisan' -

Inside the United States, Trump has ordered the National Guard into multiple US cities, in many cases against the wishes of local officials, in a bid to bring allegedly rampant unrest under control.

Abroad, Trump has ordered strikes on a series of alleged drug-smuggling vessels in the Caribbean Sea and eastern Pacific Ocean that have left more than 80 people dead since early September.

Experts say the strikes are illegal and amount to extrajudicial killings even if they target known traffickers.

A group of more than 300 former national security officials calling themselves the "Steady State" said in an open letter on Thursday that they strongly supported the six Democrats.

They said the principle of military personnel refusing unlawful orders was "not controversial. It is not partisan. It is not new. And it is the bedrock of lawful civilian control of the military."

The White House and Pentagon chief Pete Hegseth on Wednesday both slammed the message from the Democratic lawmakers.

Hegseth described it as "Stage 4 TDS," or "Trump Derangement Syndrome" -- a term used by the right to mock the president's opponents.

Trump previously evoked the death penalty in 2023 in relation to his former top US military officer Mark Milley, who became an outspoken critic of the president.

After Milley told journalist Bob Woodward that he had secretly called his Chinese counterpart amid tensions after Trump supporters stormed the US Capitol in January 2021, Trump said "in times gone by, the punishment would have been DEATH!"

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