Waltz, 50, a military veteran and a long-time Trump supporter, was re-elected to Congress last week.

He was named national security adviser – which would involve identifying and countering threats to the US. The appointment would not require Senate approval.

Waltz is a decorated Green Beret and army veteran, having served multiple tours in Afghanistan, the Middle East and Africa.

In his book, Warrior Diplomat: A Green Beret’s Battles from Washington to Afghanistan, he documented his experiences serving in the Pentagon during the George W Bush administration and in combat operations overseas.

Like Rubio, Waltz has taken a tough line on China. As chair of the Armed Services Subcommittee on Readiness, he argued the US needed to do more to prepare for conflict in the Pacific.

He has also said the US should maintain its support for Ukraine, but in recent weeks has advocated for a reassessment of US spending on aid for the war effort.

Waltz has said Nato allies should increase their defence spending, though he has not gone as far as Trump – who has reportedly suggested the US could leave the Western military alliance, to which it is the main contributor.

“Look, we can be allies and friends and have tough conversations,” Waltz said last month.

Since the 2021 withdrawal from Afghanistan, Waltz has frequently criticised President Joe Biden and the White House.

He is the second member of Congress asked to serve in the next Trump administration, which would require him to resign his office in the House of Representatives.

That could have ramifications if the Republicans end up controlling the House with a slim majority. Waltz’s resignation would cut any majority by one until a replacement could be elected.

Waltz will be the fifth national security adviser to serve under Trump, who appointed four different men to serve in the position during his first term.

Trump sacked three of them: Michael Flynn, HR McMaster and John Bolton. The latter of the three actively campaigned against Trump in the 2024 election.