Marco Rubio won his primary this week, and is now officially the Republican nominee for the U.S. Senate in Florida. Finally, a bit of good news for this gifted politician, after a rather humiliating year.

It wasn't so long ago when Rubio was the GOP's great hope. Young, charismatic, smart, Latino, with a winning personal story, he looked tailor-made for a presidential run. And so he ran. But his media-based campaign never really got traction. He ended up looking like the establishment dream candidate in an anti-establishment year. The highly polished speaker suffered what some called a "software malfunction" in the New Hampshire debate, inexplicably repeating the same talking point word-for-word four times in a row right after being needled by Chris Christie for repeating talking points.

Rubio had a brief comeback of sorts as the GOP's anti-Trump candidate. But that comeback was embarrassingly short-lived. Shortly after Rubio went a bit too far in mocking Trump (by making jokes about his penis size, even as he criticized Trump for his careless language), he lost his home state of Florida to Trump and had to fold his campaign.

The embarrassment didn't end there. When Trump became the presumptive Republican presidential nominee, Rubio half-heartedly endorsed him, a man who, only weeks earlier, he'd called a con artist unfit for office.

Then, after pledging on countless occasions that he would never, ever pursue a second term in the Senate — he would either win the presidency or retire from politics — he pursued a second term in the Senate. While that decision makes sense on the merits — it's looking like a bad year for Republicans in Florida and Rubio is by far the best candidate they have — it was yet another embarrassing flip-flop for Rubio.

All of this makes it difficult to tell exactly which office Marco Rubio is running for. Is he running for the Senate? Or is he running for president?

When asked about this, Rubio gave one of his painfully-tailored answers: "I can commit to you this, and that is that if I am running to be a U.S. senator, I am fully prepared to allow the U.S. Senate to be the last political office I ever hold." Got that? He's fully committed to being a U.S. senator — unless something better comes along.

Look: America is the land of second chances. Rubio is still young, still talented, still Latino, and he will still be all those things four years from now. Ted Cruz started running for 2020 the minute he stopped running for 2016. And a lot of Rubio's mistakes can be chalked up to inexperience.

But there's some tension between being a good senator and a good presidential candidate. Barack Obama, Ted Cruz, and Marco Rubio all accomplished virtually nothing as senators because they saw the Senate as little more than a step to the White House. Out of the class of Tea Party senators from the previous cycles — Cruz, Rubio, Rand Paul, and Mike Lee — it's telling that the one with the most impressive record, Lee, is also the one who has made clear he has no intentions of ever running for president. Working from the Senate while calculating every move with the presidency in mind stymies the sort of deal-making and position-taking that allows successful legislation to be passed.

For example, even though he's been on every side of the immigration issue, I would bet that in his heart of hearts, Rubio believes the best thing for immigration in America is to pass comprehensive legislation that includes a path to citizenship and/or legalization for a significant number of undocumented immigrants, stronger immigration enforcement, and a Canada- or Australia-style points-based skills immigration system. That's a defensible and laudable position. Maybe as a senator he can finally get that bill passed by the Senate by Speaker Ryan (or Speaker Wasserman Schultz) and signed by President Clinton.

Or he can run for the Republican nomination in 2020.

But he can't do both.

A must-read profile of Rubio by ace BuzzFeed political reporter McKay Coppins paints Rubio as a man plagued by anxiety, and whose anxiety prods him to always be running, always be on the move. Rubio got into politics as a young adult, and in whichever office he held, starting with city commissioner for West Miami fresh out of law school, he has always been aiming for the next rung of the ladder — Florida House of Representatives, speakership, Senate, president. Whatever the root of this anxiety, Rubio would do well to confront it rather than feed it.

It's time to settle down. Marco Rubio can be a great senator. Or he can run for president. But he can't do both.