Trump has asked Rep. Mike Waltz, R-Fla., to be his national security adviser, multiple sources said.

Waltz was at Mar-a-Lago on Monday, sources said.

The national security adviser is appointed by the president without Senate confirmation.

Waltz is a former Green Beret and China hawk who has emerged as a key surrogate for Trump, criticizing the Biden-Harris foreign policy record during the campaign.

The Florida Republican serves on the Intelligence, Armed Services and Foreign Affairs committees.

He has backed aid to Ukraine in the past, but demanded “conditions,” including increased spending from European allies, additional oversight of the funds and combining aid with border security measures.

Waltz, who visited Ukraine, has been a vocal critic of the Biden administration’s Ukraine policy, criticizing the White House and allies for not providing Ukraine with more lethal aid — such as MiG fighter jets — early in the conflict.

Before running for elected office, Waltz held various national security policy roles in the Bush administration, the Pentagon, and the White House.

Trump has had four different national security advisers during his first term, apart from those who served very briefly: Michael Flynn, HR McMaster, John Bolton and Robert O’Brien.

-ABC News’ Rachel Scott, Benjamin Siegel, John Santucci and Katherine Faulders