(CNN) — President-elect Donald Trump is likely to pick Florida Sen. Marco Rubio as his secretary of state, two people familiar with his thinking told CNN, as he rounds out his national security team in a second term. It was not clear as of Monday night whether Trump had formally offered Rubio the role. As of the morning, one of the sources said, the belief was that Trump was leaning toward Ric Grenell, but over the course of the day, he shifted his preference to Rubio after a number of calls and conversations with allies of the Florida senator. Grenell served as Trump’s ambassador to Germany and later as acting director of national intelligence during his first administration Until an offer is formally made, another source advised, Trump could change his mind. The New York Times first reported on Trump’s expected offer. Rubio, who was in the running to be vice president, had made it clear that he was interested in potentially joining Trump’s Cabinet if it was for the right role, several sources familiar with the process told CNN. Given his deep foreign policy experience and that he sits on both the Senate Intelligence Committee and the Foreign Relations Committee, the State Department seemed like a good fit for Rubio. The senator also hails from Florida and has a close relationship with the incoming chief of staff, Susie Wiles. A Rubio spokesperson declined to comment on the matter. The Florida senator, a China hawk and finalist for Trump’s VP, was a constant on the campaign trail during Trump’s third presidential run. After his failed GOP presidential primary in 2016, Rubio rebuilt his image in the likeness of a populist in Washington. At the same time, he sharpened his foreign policy credentials as the leading Republican on the Senate Intelligence Committee, while building relationships in his party, across the aisle and around the globe. He has used his perch as the top Republican on the Senate Intelligence Committee to take on China, introducing legislation that would block tax credits for electric vehicle batteries produced using Chinese technology and grilling the FBI director on Beijing’s influence over TikTok. In 2016, Rubio and Trump’s relationship seemed it may be beyond repair when in the closing days of his campaign, Rubio publicly attacked Trump, saying he wasn’t going to “make America great. He’s gonna make America orange,” mocking the size of Trump’s hands and calling him a “con artist” vying to take over the Republican Party. But since, Rubio and Trump’s relationship has not only thawed, it has strengthened. CNN’s Jack Forrest, Lauren Fox and Steve Contorno contributed to this report.