Rex Tillerson, the former head of Exxon Mobil Corp., is due to face tough questioning from senators at his confirmation hearing to be the next secretary of State.

The hearing in the Senate Foreign Relations Committee is expected to start Wednesday and could extend to Thursday, although the panel, headed by Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.), has not formally set the hearing date in stone.

Tillerson is a rare State nominee. He has never served in the government before, although as head of the country's largest oil and gas company for more than a decade, he has extensive experience working with foreign nations on business deals.

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He is likely to face the toughest questioning over his ties to Russia and his perceived closeness with Russian President Vladimir Putin.

Many Democrats, and some Republicans like Sens. John McCain John Sidney McCainKelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks Trump pulls into must-win Arizona trailing in polls MORE (Ariz.) and Lindsay Graham (S.C.), have been openly skeptical about Tillerson due to his Russia ties.

But Democrats are also likely to probe Tillerson's and Exxon's history on climate change.

For decades, the company sought to sow doubt about whether climate change is real and whether using fossil fuels cause it, despite reports that Exxon knew that as early as the 1970s.

Under Tillerson, Exxon shifted its stance on climate change, accepting the global consensus that humans are contributing to global warming. And the company endorsed the Paris climate deal that President-elect Trump and Republicans have blasted.

Despite those questions about Russia and climate, Corker said Friday that he believes Tillerson will sail along.

"I predict that he's going to be overwhelmingly supported," Corker said at a Christian Science Monitor event. "I predict that people are going to see what a distinguished this person is. I think they're going to see how substantial this person is."

Tillerson is part of the first wave of Trump's nominees to get a Senate hearing; five other hearings are due to take place Wednesday as well.

The chairmen of the committees responsible for considering Environmental Protection Agency nominee Scott Pruitt, Energy Department nominee Rick Perry and Interior Department nominee Ryan Zinke have not yet announced hearing dates. But those nominees could get their hearings soon, and they could be within days of Tillerson's.

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