The crowded Republican field for an open Senate seat in Georgia is still a free-for-all with less than four months until the primary, a new poll shows -- and an upset, potentially worrisome for national Republicans drafting a map to a Senate majority, is as likely as ever.

The poll, commissioned by the Citizens United Political Victory Fund, shows seven of nine candidates with some share of support, but not one with more than 20 percent.

Leading the group with 19 percent is Rep. Phil Gingrey, a doctor who has served in Congress since 2003. Two other members of Congress, Reps. Paul Broun and Jack Kingston, are competing with Gingrey for the Republican nomination; in this poll, both scored in the low double-digits, with 13 percent and 11 percent, respectively.

Running neck-and-neck with Gingrey, Broun, and Kingston is Karen Handel, a former secretary of state who ran unsuccessfully for governor in 2010. Handel received 14 percent support in the Citizens United poll.

David Perdue, a businessman and cousin to former Georgia Gov. Sonny Perdue, a Republican, rounds out the top five with 8 percent.

The GOP primary race for the seat left open by the retirement of Sen. Saxby Chambliss, a Republican, is being closely watched by Democrats, who have recruited a strong candidate in Michelle Nunn, former CEO of a major nonprofit organization and the daughter of former Sen. Sam Nunn, D-Ga. Nunn has raised money at a strong pace and will enjoy wide name recognition — but, in a state that leans Republican, the best hope for Democrats might be if a more extreme or gaffe-prone Republican were to advance to the general election, as happened in a few states in 2012.

In Missouri in 2012, Rep. Todd Akin, a Republican, posted a surprise win in his party's primary, only to torpedo his candidacy shortly thereafter with his infamous comment about "legitimate rape." Sen. Claire McCaskill, D-Mo., among Republicans' biggest targets during that election cycle, went on to win re-election.