Trump’s decision caps a lengthy process that often played out in public and exposed rifts within his transition team. It also sets Trump up for a potential fight with Congress over confirming Tillerson, who has connections with Russian President Vladimir Putin.

Trump was set to announce Tillerson’s nomination Tuesday morning. The people close to his transition team insisted on anonymity because they were not authorized to disclose the decision ahead of that announcement.

The president-elect had moved toward choosing Tillerson after a meeting Saturday, their second discussion in a week. Trump was said to be drawn to the prospect of having an international businessman serve as the nation’s top diplomat.

But the prospect of Tillerson’s nomination sparked immediate concern on Capitol Hill. Sen. Marco Rubio, R-Fla., wrote on Twitter that “being a ‘friend of Vladimir'” was not an attribute he was seeking in a secretary of state.

In a weekend interview with “Fox News Sunday,” Trump pointed to Tillerson’s deep relations with Moscow as a selling point. As Exxon Mobil’s head, he maintained close ties with Russia and was awarded by Putin with the Order of Friendship in 2013, an honor for a foreign citizen.

“A great advantage is he knows many of the players, and he knows them well. He does massive deals in Russia. He does massive deals for the company,” Trump said.

A native of Wichita Falls, Texas, Tillerson came to ExxonMobil as a production engineer straight out of the University of Texas at Austin in 1975 and never left. Groomed for an executive position, Tillerson came up in the rough-and-tumble world of oil production, holding posts in the company’s central United States, Yemen and Russian operations.

For more on ExxonMobil, watch Fortune’s video:

Trump also seriously considered Mitt Romney, the 2012 GOP presidential nominee, for the job. Romney said late Monday that he was honored to be considered, signaling that he was being passed over for the high-profile Cabinet position.

Trump’s decision to consider Romney, who fiercely criticized him during the campaign, was strongly opposed by some members of his transition team, who saw the potential nomination as a betrayal to longtime supporters.

Romney blasted Trump as a “fraud” during the campaign, but was full of praise for the president-elect after they discussed the State Department post over a private dinner in Manhattan. He wrote in a Facebook post Monday night that his discussions with Trump were “enjoyable and enlightening.”

“I have very high hopes that the new administration will lead the nation to greater strength, prosperity and peace,” Romney wrote.