Trump transition: Trump announces Matt Gaetz as attorney general, Marco Rubio as secretary of state

President-elect Donald Trump is expected to announce his intention to nominate Sen. Marco Rubio, R-Fla., for secretary of state, according to multiple sources familiar with the matter, ABC News reported.

Rubio, 53, has served in the Senate since 2011. He is currently the vice-chair of the Senate Select Committee on Foreign Intelligence and also sits on the chamber's Committee on Foreign Relations.

Several long-serving State Department officials tell ABC News they respect Rubio's extensive foreign policy experience and view him as unlikely to overly politicize the secretary of state role.

Rubio was also said to be favored for the role by Trump's chief of staff and veteran Florida political operative Susie Wiles, potentially helping the lawmaker edge out loyalists from the first Trump administration like former acting Director of National Intelligence Richard Grenell and former National Security Adviser Robert O'Brien.

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 confirmation by the Senate.

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

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

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

Waltz, who has visited Ukraine, was a vocal critic of the Biden administration's policy towards Ukraine, criticizing the White House and allies for not providing Ukraine with more lethal aid -- such as MiG fighter planes -- earlier in the conflict.

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

Trump had four different national security advisers during his first term, outside of those who served very briefly: Michael Flynn, H.R. McMaster, John Bolton and Robert O'Brien.

Melania Trump is not expected to travel to Washington with President-elect Donald Trump on Wednesday, two sources told ABC News.

First lady Jill Biden had extended an invite to Melania Trump for a meeting, according to the sources. In 2016, Michelle Obama had hosted Melania Trump at the White House.

The Trump campaign declined to comment. ABC News has reached out to the first lady's office for comment.

Robert F. Kennedy Jr. has continued to broadly advise Trump and the transition team on health-related appointments and has been in discussions to possibly fill a major role in the next administration, sources familiar with the matter told ABC News.

While sources caution that a role has not been finalized, RFK Jr. has been discussed as a potential candidate for the next secretary of Health and Human Services. But other roles are also on the table, including a broad "czar"-like position that would advise on policy and personnel decisions in other health arenas, the sources said.

RFK Jr. has been in active discussions with the transition team since Trump's election victory last week. He's been spotted at Trump's Mar-a-Lago club multiple times and has been engaging in presentations which include candidates for specific Cabinet and health-related jobs, sources said.

He has spent hours with the co-heads of Trump's transition team -- billionaire Howard Lutnick and Linda McMahon -- in addition to others at Mar-a-Lago such as Trump's son Donald Trump Jr.; investor and donor Omeed Malik; Tucker Carlson; and Del Bigtree, RFK Jr.'s former campaign spokesperson who produced a documentary called "Vaxxed: From Cover-Up to Catastrophe."