Rex Tillerson, the apparent front-runner to become President-elect Donald Trump’s secretary of state, can expect a very tough job interview.

Tillerson, the chief executive of Exxon Mobil, is one of the few Americans who can call Russian President Vladimir Putin a personal friend. Tillerson has represented Exxon’s interests in Russia since the 1990s and has spent years lobbying the U.S. government to ease sanctions against the country.

Although Trump’s transition team said they won’t formally announce their pick until later this week, Tillerson met with the president-elect for more than two hours on Saturday and is said to be “in a different league” from the other people being considered for the job, the New York Times reported.

But Tillerson’s close ties to Russia are making some prominent Republican hawks nervous. “It’s a matter of concern to me that he has such a close personal relationship with Vladimir Putin,” Sen. John McCain said on CBS’ “Face the Nation” on Sunday. “That would color his approach to Vladimir Putin and the Russian threat.” In 2013, Putin personally awarded Tillerson the Order of Friendship, one of Russia’s highest honors given to foreign civilians.

Sen. Marco Rubio also slammed Tillerson in a semi-veiled tweet Sunday. “Being a ‘friend of Vladimir’ is not an attribute I am hoping for from a Secretary of State,” the Republican said.

Rubio is a member of the Senate Foreign Relations Committee, which has to vote on Tillerson before the entire Senate confirms him. Republicans currently hold 52 seats in the chamber, and if Democrats unify against him, Tillerson will need all but two of them to vote for him with Vice President-elect Pence breaking the tie.

Tillerson isn’t the only one of Trump’s expected State Department picks who will face a difficult Senate confirmation process. Republican Sen. Rand Paul, also a member of the Foreign Relations Committee, said he would block the nomination of former ambassador John Bolton to the No. 2 position in the State Department.

“John Bolton doesn’t get it. He still believes in regime change. He’s still a big cheerleader for the Iraq War,” Paul said Sunday during an appearance on ABC’s “This Week.” “John Bolton is so far out of it and has such a naive understanding of the world.”

On Tillerson, however, the libertarian senator said he’d “reserve judgment.”

Republican Sen. Lindsey Graham also expressed discomfort with Tillerson and his connections to Russia. “I don’t know the man much at all, but let’s put it this way: If you received an award from the Kremlin, [an] Order of Friendship, then we’re gonna have some talkin’,” Graham told the Washington Post. “We’ll have some questions. I don’t want to pre-judge the guy, but that’s a bit unnerving.”

Democrats are also uneasy about Tillerson filling the job of top diplomat. Senator Ben Cardin, the ranking Democrat on the Foreign Relations Committee, said on CNN Sunday he was “concerned about his [Tillerson’s] relationship with Russia. We want to make sure that the secretary of state is a person who represents America.”

Trump cited Tillerson’s close relationship with Putin and Russia as an asset, not a concern, for the job. During an interview with “Fox News Sunday,” the president-elect called Tillerson a “world-class player” who does “massive deals in Russia.”

But Tillerson could be helped by a numbers game. Democrats will have to pick their battles when it comes to fighting Trump’s appointments, and they’ve already expressed their distaste with his choice for attorney general, Health and Human Services, Environmental Protection Agency, and Treasury secretary. Indeed, no Republican lawmaker has said outright they would oppose Tillerson. Senator Bob Corker, the Republican chairman of the Foreign Relations Committee, tweeted that he is a “very impressive individual.”

The biggest deal Tillerson signed with Russia, which took place in 2011, allowed Exxon and Russia’s state-run oil company, Rosneft, to jointly drill for oil in Russian-controlled areas of the Arctic, the Black Sea, and Siberia. Tillerson received the Order of Friendship shortly thereafter.