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The U.S. Senate voted Wednesday to confirm ExxonMobil CEO Rex Tillerson as the next secretary of state.

The vote in favor of President Trump's pick for the key cabinet post fell mostly along partisan lines, with Republican lawmakers who have voiced concerns like Senators Marco Rubio, John McCain and Lindsey Graham joining fellow GOP members in affirming the nomination.

Tillerson needed a simple majority — 51 senators — for confirmation. The final vote was 56 in favor, 43 against.

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Three Democrats voted in favor of Tillerson, including Senators Joe Manchin, Heidi Heitkamp, and Mark Warner. Angus King, an Independent who caucuses with the Democrats, also voted in for Tillerson.

Tillerson was sworn in by Vice President Mike Pence with Trump by his side during a ceremony in the Oval Office later Wednesday. Trump praised Tillerson for his experience and said the new secretary of state was "respected all over the world," according to a transcript released by the office of the White House press secretary.

"You bring the unique skills and deep, deep insights — and I’ve gotten to see it firsthand — into foreign diplomacy our nation needs to foster stability and security in a world too often trapped — and right now it’s trapped — in violence and in war," Trump said of Tillerson.

Former ExxonMobil executive Rex Tillerson testifies during his confirmation hearing for Secretary of State before the Senate Foreign Relations Committee on Capitol Hill in Washington, D.C., Jan. 11, 2017. Saul Loeb / AFP - Getty Images

It was Tillerson's contacts with Russia and strongman Vladimir Putin that raised alarms among some Republicans. Among other things, Tillerson was given the Order of Friendship award by Putin.

But after a sit-down with the skeptical senators, McCain said he would back Tillerson.

"Listen, this wasn't an easy call, but I believe when there's doubt, the incoming president gets the benefit of the doubt," McCain said earlier this month on ABC's "This Week."

Rubio was holding out on support out of concerns that Tillerson refused to say that he would support the continuation of sanctions against Russia over their aggression in Ukraine — and because Tillerson refused to say he would support sanctions against Moscow for meddling in the U.S. presidential election.

Amnesty International said "the eyes of the world" will be on Tillerson.

"As Secretary of State, Rex Tillerson’s priority must be human rights," the group said. "However, during his confirmation hearings, he seemed to balk at acknowledging governments that we have long known to turn a blind eye toward human rights. His previous business deals have shown that he has no qualms about working with regimes with appalling human rights records.”