Over a third of the country — 17 states — use an open primary format for voting.

An "open primary" is one in which voting is not restricted only to the registered members of a particularly party. In Florida, for example, when the GOP presidential race was at its apex back in late January, only registered Republicans could cast a vote for Mitt Romney, Newt Gingrich or anyone else still in the race. Independents and Democrats who wanted to back one of those candidates were out of luck.

Former Democratic state Senator Dan Gelber of Miami Beach supports bringing the open primary concept to Florida, and he got a big-named backer this weekend in former Governor Charlie Crist, who came out in favor of open primaries on Chuck Todd's MSNBC chat fest The Daily Rundown on Monday.

"If you have open primaries where people in some states can already do this, whether you're a Republican, an independent or a Democrat, on primary election day you can decide in that party's primary, even if it's not your own," Crist said.