Republican Thomas Massie will force impeachment vote on Defence Secretary Pete Hegseth

A Republican congressman plans to force a vote in the House of Representatives this week to impeach Defence Secretary Pete Hegseth, alleging he has violated the US Constitution.

"By engaging in hostilities in Iran for more than 90 days without congressional authorization, Secretary Hegseth is breaking the law and must be held accountable," Representative Thomas Massie said.

The effort will likely fail, given Republicans will remain in power in Congress until January. But Massie says he wants to push President Donald Trump to fire Hegseth before Democrats can launch their own impeachment process.

Hegseth, who will hold a news conference on Tuesday about Massie's move, said he was not concerned.

Massie formally introduced the articles of impeachment in a resolution on the House floor on Monday afternoon.

"We're not worried about that," Hegseth said when asked by reporters about the impending resolution earlier on Monday, adding he would hold a news conference Tuesday morning "on that very topic".

Hegseth's last news conference was in May.

Massie, who lost re-election earlier this year, has been critical of Trump and the war in Iran since it started nearly nine months ago. He is known across the country for also pushing the administration to release federal files on the deceased sex offender Jeffrey Epstein.

The Kentucky congressman first introduced impeachment articles in September and is now pressing for a vote in the wake of Republicans losing control of both the House and Senate in last week's midterm elections. He has said his push to rid the administration of Hegseth is meant to prevent a Democrat spectacle next year.

"My effort to impeach Secretary Hegseth is a much gentler version of what's coming when the Democrats assume control of the House and Senate next year," Massie also said in a statement. "They will hold hearings and trials."

"President Trump should replace Secretary Hegseth now while he can still get a replacement confirmed in the Senate," he also said.

Impeaching a cabinet secretary is very rare. The impeachment must be approved by both chambers for the secretary to be removed from office. As with presidential impeachments, the House would first hold a vote on charges against Hegseth and the Senate then would conduct a trial to decide whether to acquit or convict.

The House has voted to impeach only two cabinet members in US history, but the Senate did not agree on either one.

Now Massie has introduced his resolution, Speaker of the House Mike Johnson must schedule a time to consider it within two days. Along with voting on the resolution directly, the House has the options to vote to refer it to committee or to set it aside.

Massie will likely have the support of the Democrats in the House, with that party's leader, Hakeem Jeffries, saying on Sunday that he is a "hard yes" on impeachment. But Massie would still need to win over members of his own party.

Peter Loge, a professor of public affairs at George Washington University, told the BBC that the impeachment measure is "likely to pass the House because the Republican majority is so slim".

"And there are enough angry Republicans that more than enough Republicans are gonna simply not show up to vote," he added.

Currently, there are 218 Republicans and 214 Democrats in the House.

Loge also says the chances that Hegseth will survive until the end of Trump's term are "pretty slim", and he thinks it's more likely that the president will remove the secretary than lawmakers will vote to impeach him.

The Senate requires a two-thirds vote to convict, a high threshold that would be hard to meet in the current congressional term. When the Democrats take over in January, they still will not have enough seats to convict Hegseth without Republican support – even if Alaska and Mississippi end up with Democratic senators once all ballots are counted.

The House has passed a War Powers resolution - a measure seeking to halt Trump from taking further military action in Iran - multiple times this year, with Massie's support. The Senate also passed a War Powers resolution over the summer.

But Massie's disagreement with Hegseth goes beyond Iran, he said in the statement.

He accused Hegseth of intimidating critics of the Trump administration, kidnapping foreign leaders and ignoring congressional war powers resolutions.

Loge suspects the negative attention Hegseth has attracted might be what prompts Trump to fire him, saying the secretary "has been pushing the limits of decency and legality for a long time".

"Secretary Hegseth is a big personality, and I'm not sure I'd want to be a big personality that's drawing attention from President Trump these days," Loge said. "That's not a way to guarantee job security."

Top House Democrat 'a hard yes' on impeaching Hegseth

White House denies Hegseth and Rubio to leave jobs after Republican election losses