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.

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

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.

The secretary of state is appointed by the president with the consent of the Senate.

-ABC News' Katherine Faulders and Shannon Kingston

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.

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

A volunteer-run effort on Robert F. Kennedy Jr.'s website has begun crowd-sourcing ideas for appointments in Trump's administration.

A website titled "Nominees for the People" gives anyone the chance to submit names of people they'd like to see join the administration.

"President Trump and Robert F. Kennedy Jr. want your help nominating people of integrity and courage for over 4,000 appointments across the future Trump administration," the website reads.

Stefanie Spear, a Kennedy spokeswoman, told ABC News that the crowd-sourcing effort is "a grassroots initiative run by volunteers," and is not actually spearheaded by Kennedy, although the page uses the "mahanow.org" URL that Kennedy's official campaign website adopted after he exited the race.

"We’ve always offered space on our website to our grassroots movement," Spear said.

This post has been updated to reflect that the crowd-sourcing effort is a volunteer-run effort.

-ABC News' Sasha Pezenik

Former Immigration and Customs Enforcement Director Tom Homan, Trump's newly announced "border czar," said his main priority will be overseeing and formulating Trump's long-vowed mass deportation strategy while consolidating decisions related to border security.

"Everybody talks about this mass deportation operation. President Trump talks about. I'll oversee that and come up with a strategy for that," Homan said during a lengthy interview with his hometown television station WWNY on Monday.

Homan said Trump's mass deportations is "going to be a targeted enforcement operation, concentrating on criminals and national security threats first."

He acknowledged that the deportations would be costly but argued the policy would "save the taxpayers a lot of money."

Homan said he does not plan to "separate women and children" but acknowledged that deporting alleged criminals would result in breaking up families.

"When we arrest parents here, guess what? We separate them. The illegal aliens should be no different," Homan said.

Homan also said worksite enforcement -- an aspect of immigration policy focused on unauthorized workers and employers who knowingly hire them -- is "going to get fired back up."

"Under President Trump, we're going to work it and we're going to work it hard," he said.

-ABC News' Peter Charalambous