Leaving the hearing after his third round of questioning, Mr. Rubio would not commit to supporting — or opposing — Mr. Tillerson, telling reporters that he was “prepared to do what’s right” even if fellow Republicans lined up behind Mr. Trump’s nominee.

Tillerson favored arms for Ukraine

Mr. Tillerson also told the committee that if he had been serving in office when Russia annexed Crimea in 2014, he would have recommended that the United States provide arms and intelligence support to the government of Ukraine, and said the Obama administration’s reaction was viewed in Moscow “as a weak response.”

Mr. Tillerson’s prescription came in the opening two hours of his confirmation hearing, where he went out of his way to portray himself as a hard-liner in confronting Russia — an effort to defuse questions about his business relationships with Mr. Putin.

But in doing so, he put himself in direct opposition to the position taken by Mr. Trump, who said in interviews with The New York Times last year that he doubted the utility of the sanctions the United States led against Russia.

Tethered to Trump

As the questioning wore on, some senators nodded at the lengthy — and, at times, rocky — proceedings. “I’m glad you came back after lunch, Mr. Tillerson,” joked Senator Jeanne Shaheen, Democrat of New Hampshire.

She thanked Mr. Tillerson for outlining his efforts to disentangle himself from Exxon Mobil while seeking a role in government. But she added that his approach “stands in stark contrast to what we heard from President-elect Trump today” about his own business conflicts, referring to the news that Mr. Trump will not divest himself of his business empire.

Ms. Shaheen also asked Mr. Tillerson to weigh in on some of Mr. Trump’s most explosive campaign positions, like calls for a ban on Muslim immigration.