4. Florida

The seat vacated by former GOP presidential hopeful Marco Rubio is up for grabs as both parties are still figuring out who will emerge as their standard bearers.

Democrats have a slight upper hand, as the party’s establishment continues to rally behind Rep. Patrick Murphy (D-Fla.). His primary opponent, Rep. Alan Grayson (D-Fla.), is under fire over his hedge funds and Senate Minority Leader Harry Reid (D-Nev.) has called on the liberal firebrand to drop out.

But for Republicans, a crowded field of five hastaken shape. The conservative Club for Growth backed Rep. Ron DeSantis (R-Fla.) while Florida Lt. Gov. Carlos López-Cantera got a huge boost from Miami billionaire Norman Braman who will helm his campaign’s finance team.

Rep. David Jolly (R-Fla.) and businessmen Todd Wilcox and Carlos Beruff are also running.

A poll from earlier this month found both Democratic Senate candidates leading the top three GOP candidates in most head-to-head general election match-ups.