And so we have come again to a moment of testing for Marco Rubio.

His very public reservations over Donald Trump’s nominee for secretary of state, Rex Tillerson, have quickly put the Florida senator back at the center of attention. But by stepping out and threatening to derail Tillerson’s nomination with a key vote on the Foreign Relations committee, Rubio has also raised old and persistent questions about his core character.

One year ago, many would have predicted that Rubio would be in Washington this week preparing to be sworn in as the nation’s 45th president. The Republican presidential primary had not yet begun, and many believed that Rubio would ultimately win the nomination and defeat Democrat Hillary Clinton.

Instead, the 45-year old lawmaker is now entering his second six-year term as a senator, after reversing earlier statements that he would not return to the Senate if he lost the GOP primary. He had a decidedly mixed first term. In the broadest sense, the first three years were a steady ascent upward, until the immigration bill that Rubio championed in 2013 fell apart that summer. Since then, Rubio has been brought down to earth, first by talk radio and then by Trump, who belittled and humiliated him last year.

And it is the questions about Rubio’s political instincts, maturity, toughness and conviction during that first moment of testing that remain unanswered after last year’s presidential campaign.

Rubio’s skills and assets are unquestioned: He is an articulate and passionate orator who performs well on TV, he exudes charisma and he is highly ambitious. His record on policy lacks any red-letter accomplishments, but he has worked hard to lead the GOP on foreign policy and family-friendly economic proposals.

Sen. Marco Rubio participates in a reenacted swearing-in with Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol. (Photo: Aaron P. Bernstein/Getty Images)

His push for immigration reform in 2013 showed both courage and determination, as he moved quickly to lead the GOP after Mitt Romney’s disappointing 2012 loss. But he overestimated the amount of goodwill for him on the right and then found himself the public face of a bill that conservatives hated, and seemed to conclude that Democrats like Sen. Chuck Schumer, D-N.Y., had used him to sell a bill that ultimately was a nonstarter for the grassroots.

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Rubio’s full and hasty retreat from the legislation made him look craven. He looked to some like he was constantly reacting to public opinion rather than staking out a path that he believes in, factoring in the politics and then fighting for his position until the battle was won or lost.

In his presidential campaign, Rubio again fell short. He and his strategists ran a so-so campaign that prevented him from breaking out from the pack in the fall, he could not find an effective way (like all the other candidates) to take on Trump as the businessman gathered momentum, and then, just as he was poised to win New Hampshire and possibly develop an unstoppable head of steam, he suffered a debilitating breakdown in a debate.

During an infamous debate moment, Rubio cemented the core concern of many Republicans who wanted to vote for him. Under pressure from New Jersey Gov. Chris Christie, he went into robot mode, repeating manufactured talking points just as Christie was hammering him for doing exactly that. In late February and early March ahead of the Virginia primary, Rubio hit his second campaign sprint — in which he drew real blood from Trump but also sank to Trump’s level by mocking the size of his genitals — further convincing primary voters that he lacked seasoning, needed more time to mature, was too young, and so on.

Rex Tillerson and Sen. Marco Rubio at Tillerson’s confirmation hearing. (Photos: Joe Raedle/Getty Images/Joshua Roberts /Reuters)

And so now, Rubio faces two challenges with the Tillerson confirmation hearing. Anytime he maneuvers into the spotlight, he is accompanied by a chorus of second-guessing about his motives. Is this all just politics and positioning? Rubio seemed to acknowledge this when asked about how he’ll decide to vote: “I’m prepared to do what’s right,” he said.

And then there’s his second challenge: his decision on whether to ultimately vote for or against Tillerson. Does he feel compelled to follow up his tough questioning of Tillerson on Wednesday by showing he meant what he said, and that it wasn’t just a public relations ploy? He risks overreaching or miscalculating if he ends up sinking Tillerson’s nomination simply to prove his strength.

Ana Navarro, a Florida political consultant and a friend of Rubio’s, told me she thought Rubio’s approach to Tillerson was “brilliant.”

“He was in less than relative obscurity after the Trump election and has put himself back in the spotlight, has emerged as the crucial Republican vote, and he is speaking passionately about a subject matter about which we all know is near and dear to his heart,” Navarro said. “He’s been standing up against communism and oppression, against Putin, against the Castros, for his entire career. So I think he raised the profile of the issues that are important to him, and raises his own profile and political stock.”

Navarro added: “Up until three days ago, when was the last time any of us had talked about Marco Rubio? All of a sudden he’s on the ticker tape of cable news. His songs are being played on the radio again,” she said. “I had forgotten just how good this guy is politically.”

But Rubio’s political skills have never been in question, particularly when it comes to finding a way into the conversation. It’s his leadership that people have wondered about.

How Rubio votes on Tillerson won’t make or break his career, of course. Far from it. But how he votes and how he explains it will give us our first taste of whether his trip through the campaign crucible has made him a more formidable politician or not.

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