Marco Rubio for vice president? He says no, and for good reason.

Marco Rubio, the Republican junior senator from Florida, is young, charismatic, and serious about policy. And given his Hispanic heritage, he could be pure gold on his party’s presidential ticket.

That’s why, even before he had won his Senate seat last November, he was already on the presumed short list for running mate of the eventual Republican presidential nominee in 2012. The GOP must do better among Hispanic voters to recapture the presidency; in 2008, President Obama won two-thirds of that fast-growing demographic group. What’s more, Senator Rubio could help deliver Florida – the nation’s biggest swing state – to the Republicans.

There’s only one problem: Rubio really, truly does not seem to want to be on the ticket.

“I am not going to be the vice presidential nominee,” Rubio said at the Washington Ideas Forum at the Newseum in Washington on Wednesday night. “The answer is going to be no.”

We know, we know, that’s what they all say. No one wants to run for vice president until, voilà, they’ve agreed to be on the ticket. Rubio has been asked plenty of times in the past about running for veep, and has always said “no.” But now that he has the better part of a year as senator under his belt, it’s possible to see where all this could be going.

Rubio indeed has potential to appear someday on his party’s presidential ticket – but maybe he’s holding out for the top of the ticket. At barely 40, Rubio has plenty of time to make that leap.

But let’s say he were to be the GOP running mate in 2012.

If the ticket loses, then he looks like a loser who overreached after barely joining the Senate.

If the ticket wins, then he’s vice president – probably the end of any ambition toward becoming president. Current (or former) vice presidents hardly ever reach the presidency, except when the president dies in office or resigns.

If Rubio does have presidential ambitions, the reasoning goes, then why attach his star to someone else’s? More likely, he’s better off waiting to run for higher office when he has more seasoning in national and international policy – and when his four young children are a little older.

Often described as the Republicans’ Obama – young, charismatic, minority – he may prefer to follow the current president’s path and run in his own right.

“There’s something very interesting about [Rubio], and that is that he is much better than most politicians at pacing himself,” says Susan MacManus, a political scientist at the University of South Florida in Tampa. “You’ll notice that even when he could have been on every news program every hour, he hasn’t done that.”

“A lot of people look at him and say, why should he settle for No. 2 when he could be No. 1 in a few years?” Ms. MacManus adds.

[Editor's note: The photo caption originally stated Mr. Rubio spoke at the Newseum on Thursday. It was actually Wednesday.]