Republican heavyweights Mitt Romney and Jeb Bush are already out shaking the money trees for possible 2016 presidential runs, and now Florida Sen. Marco Rubio is putting out the word that he is, too.

His Reclaim America PAC has hired prominent fundraiser Anna Rogers. His major donors are gathering in Miami Beach Friday and Saturday for a "Team Rubio 2016" political update and finance committee meeting. Rubio is featured Sunday at the billionaire Koch brothers' " American Recovery Policy Forum" in Palm Springs, along with fellow senators and presidential hopefuls Ted Cruz and Rand Paul. Then Rubio will spend next week in California attending fundraisers, and a big part of February on a book tour that will take him to all the early-voting-primary states.

Of course, actively jumping into fundraising doesn't necessarily improve Rubio's odds — or even the likelihood that he will ultimately run.

He's still in his first term in the Senate after serving two years as Florida House speaker. He faces a crowded field of rivals, led at the moment by 2012 nominee Romney and former Florida Gov. Bush. Romney has proven he can raise $1 billion for a presidential run, and Bush has set upon an aggressive fundraising push that will include 60 finance events by the end of March.

Given those challenges, the obvious question arises: Why would Rubio run? In reality, though, a better question might be: Why wouldn't Rubio run?

A full year before the first voters are set to cast ballots, there are a number of good reasons for Rubio to go ahead with a presidential bid right now, at least for the coming months.

Here are five:

Practice makes perfect

Running for president isn't easy. It's a big country, and even when focusing on the early-voting states for campaigning and the big-money states for fundraising, a presidential bid is a costly, time-consuming, difficult production — which helps explain why many of those who have won their party's nomination have done so only after trying and failing in previous attempts. Ronald Reagan, George H.W. Bush, Bob Dole, Al Gore and Mitt Romney all come to mind. Running now, even in the likely event that Rubio falls short, still adds to his email and fundraising lists — way more than just running for re-election does.

The money is just as green for a Senate run

Money raised by Rubio's leadership PAC can be used by Rubio as he explores a presidential run — or it can be used as he contemplates a run for re-election in 2016. If Rubio gets to the point where he creates an actual presidential campaign account and then winds up not running, Federal Election Commission rules allow any money left over to be transferred to Rubio's Senate account (subject to individual contributor limits). Similarly, if Rubio's allies were to create a superPAC that's not technically under his control, presumably they would be in sync with his goals and switch over to support his run for re-election, should he ultimately do that. As to his statements that he will not pursue both offices at once — he wouldn't have to. He could run for president now, decide later this year to give up on that goal ... and then some months later announce that an outpouring of support from Floridians has persuaded him to seek re-election, after all. Florida's filing deadline for federal candidates is not until May 2016. Rubio would have plenty of time for a graceful transition.

David Rivera

The former Florida congressman is facing a federal investigation into his 2012 re-election bid. A friend of Rivera has already been convicted of steering money to a sham candidate in the Democratic primary that year, and that friend has been talking to prosecutors about Rivera's role. Unfortunately for Rubio, Rivera was his closest confidant and top lieutenant during Rubio's years in the Florida House. The two even co-owned a home in Tallahassee, on which a bank started foreclosure proceedings after they missed a number of payments owing to a dispute over the mortgage terms. Rubio has not been implicated at all in Rivera's 2012 problem, but their association will no doubt be an issue Rubio's opponents will use in a presidential run. But on a subsequent presidential run, Rubio could shrug off queries about Rivera as old news — as a topic that's been thoroughly vetted previously.

Sell, sell, sell

Rubio is out with a new book, American Dreams. And while someone like Romney, whose net worth is in the neighborhood of a quarter-billion dollars, may not need the money, Rubio probably could. He's only 43 and has spent most of his years since leaving law school in elective office. The $174,000 salary for members of Congress is more than triple the median household income, but it must pay for running two households, one in pricey Washington, D.C., and one in almost-as-pricey Miami. Which book is more marketable: one by a senator who's already settled on seeking a second term? Or one by a presidential aspirant? (Granted, most books don't make a ton of money. But $4 a book selling, say, 20,000 copies? That's not so shabby.)

The Naval Observatory isn't so bad

Running to be the chief executive of the United States when still in your first term in the Senate might be a stretch — particularly when your party has made President Obama's similar inexperience a major critique. But the No. 2 job on the ticket? Some of the features that make Rubio so attractive as a presidential candidate — his Cuban-American ethnicity, his youth, his presumed strength in a key swing state — might be just as attractive as a running mate. (That is, if the nominee is anyone other than Bush. Bush has a Mexican-born wife, is fluent in Spanish and is arguably a stronger statewide candidate in Florida than Rubio.) And then, win or lose, Rubio would be considered a top contender either four or eight years later. So if 1600 Pennsylvania Ave. is out of reach this time, the house a couple of miles to the northwest maybe isn't a bad second choice.

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