This evening, U.S. Senator Marco Rubio (R-FL) officially announced that he is running for President. He joins fellow senators Ted Cruz and Rand Paul as the first Republican candidates in what is likely to be a crowded field.
Rubi, Paul and Cruz are all in their first term in the Senate. Rubio and Paul were elected in 2010, while Cruz was elected in 2012. This causes a dilemma for Rubio and Paul; Ted Cruz is in the middle of his term, and won't risk his Senate seat by running for President, while 2016 is the end of Rubio's and Paul's term.
It is against state law in both Kentucky and Florida to be on the ballot for more than one office. Rand Paul looks like he will run for both President and Senate, and appears to be getting around that by having the Kentucky GOP move to a caucus rather than a primary, thus avoiding his being on the primary ballot for two offices. Rubio has said he would only run for President or Senate -- not both, like Democrats Joe Biden (in 2008) and Joe Lieberman (in 2000) did.