MIAMI (CBSMiami) – Republican presidential front-runner Mitt Romney is looking to wrap up the nomination process as soon as Tuesday’s Wisconsin primary. Once that happens, the focus will turn to his vice-presidential selection, but candidates for that job might want to think a long time before accepting it.

The last time a losing vice-presidential nominee was able to come back and win the presidency in a later election was Franklin D. Roosevelt. FDR ran as a vice-presidential candidate with James M. Cox in 1920 with their ticket losing to Warren G. Harding. Twelve years later, FDR won the presidency.

It serves as a cautionary tale for Florida Senator Marco Rubio who is widely considered to be a front-runner for the vice-presidency. Senator Rubio has the characteristics any president would look for including being hard to fluster, calm, young and energetic, and appeals to his party’s base.

Rubio has repeatedly turned away speculation that he would be the vice-presidential pick, but the talk surrounding him has only grown after he endorsed Romney for the presidency.

Still, Rubio may be trying to fight history if he’s not completely sure that Romney can knock off President Barack Obama in November.

Out of the 12 presidents since FDR, five were former vice-presidents (Harry S. Truman, Lyndon B. Johnson, Gerald Ford, and George H.W. Bush). Interestingly enough, out of that list, four of the five ascended to the presidency due to death, assassination, or resignation.

Some vice-presidents won their party’s nomination but couldn’t win the top job including Hubert Humphrey, Walter Mondale, and Al Gore. The losing vice-presidential candidate has often times ended up in much worse shape than when they started including: John Edwards, Joe Lieberman, and Lloyd Bentsen.

If Rubio isn’t 100 percent convinced Romney can win in November, his best bet may be to stay on the sidelines and wait for 2016 when he could run as a presidential candidate on his own.

Rubio isn’t the only candidate for the vice presidency. The full list of potential GOP vice-presidential candidates includes: Louisiana Gov. Bobby Jindal, Wisconsin Rep. Paul Ryan, New Jersey Gov. Chris Christie, South Dakota Sen. John Thune, and former Minnesota Gov. Tim Pawlenty.

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