Sen. John McCain (R-Ariz.) says he is troubled by President-elect Donald Trump secretary of State pick Rex Tillerson’s ties with Russia.

“I and several of my colleagues have concerns about Mr. Tillerson, and some of his past activities, specifically his relationship with [Russian President] Vladimir Putin,” McCain said Thursday, according to Reuters.

“I have concerns, but at the same time I’m certain we will give Mr. Tillerson an opportunity to make his case about why he is qualified to be secretary of State.”

{mosads}McCain said he is worried about Tillerson’s opposition to sanctions against Russia for its 2014 annexation of Crimea.

He added that the U.S. must reassure voters that Russia had no influence over November’s presidential election.

“I agree with the president-elect that we need to get on with our lives — without having elections being affected by any outside influence, especially Vladimir Putin, who is a thug and murderer,” said McCain.

Tillerson may face an uphill confirmation battle due to deep skepticism in the Senate over his past business dealings in Russia.

The Senate Foreign Relations Committee has 10 Republicans and nine Democrats — so the committee could reject Tillerson if one Republican joins all the Democrats in opposing him.

Tillerson, the CEO of Exxon Mobil Corp., negotiated an energy partnership with Putin in 2011 that the Russian leader said could be worth $500 billion.