Florida Senator Marco Rubio became the third Republican Senator to join the 2016 presidential race on Monday, joining Kentucky's Rand Paul and Ted Cruz of Texas. Rubio held a call with donors Monday morning to let them know he was running. A public announcement will come this evening at downtown Miami's Freedom Tower.
Rubio has averaged about 7% in recent Republican preference polling putting him in the middle of the pack, trailing his political mentor Jeb Bush who is polling in the mid-teens in a crowded field of prospective nominees. Bush has not yet declared his candidacy for 2016.
There hasn't been a great deal of early polling for a general election match-up between Rubio and Hillary Clinton; that link will let you track the race and also links to an interactive map that looks at polling + 2012 results in unpolled states.