Arizona Sen. John McCain said Sunday he would support Rex Tillerson's nomination for secretary of state.

McCain had said in the last few weeks that he was leaning toward backing Tillerson, but still had concerns about the former ExxonMobil CEO's ties to Russian President Vladimir Putin.

McCain first announced his support for Tillerson Sunday morning on ABC's "This Week." The senator followed up with a written statement, issued jointly with Republican Sen. Lindsey Graham:

"After careful consideration, and much discussion with Mr. Tillerson, we have decided to support his nomination to be Secretary of State. Though we still have concerns about his past dealings with the Russian government and President Vladimir Putin, we believe that Mr. Tillerson can be an effective advocate for U.S. interests.
"Now more than ever, with America's friends growing more discouraged and our enemies growing more emboldened, we need a Secretary of State who recognizes that our nation cannot succeed in the world by itself. We must strengthen our alliances and partnerships across the globe, and marshal them to defend our shared vision of world order. It is the American people more than anyone else who have benefited from this long tradition of U.S. global leadership. The views that Mr. Tillerson has expressed, both privately and publicly during the confirmation process, give us confidence that he will be a champion for a strong and engaged role for America in the world."

McCain and Graham's support for Tillerson assures President Donald Trump that Tillerson will win confirmation by the full Senate, even if he doesn't get a stamp of approval from the Senate Foreign Relations Committee, where GOP Sen. Marco Rubio is holding out against the nomination.

The committee is expected to vote Monday.

"Listen, this wasn’t an easy call," McCain said Sunday on "This Week," but I also believe that when there’s doubt, the incoming president gets the benefit of doubt, and that’s the way I’ve treated every president.”

But when asked by "This Week" moderator George Stephanopoulos whether he had "utmost confidence in President Trump," McCain responded: "I do not know."

McCain has clashed with Trump over the new president's apparent coziness with Russia and praise of Putin, whom McCain has branded as a "thug."

In his role as ExxonMobil's CEO, Tillerson was awarded Russia's Order of Friendship by Putin. During his confirmation hearing two weeks ago, Tillerson hedged on any criticism of the Russian president.

Three weeks ago, when McCain was asked whether he could support Tillerson's nomination, he told reporters: "Sure. There's also a realistic scenario that pigs fly."

A McCain aide later said the senator was joking.