Rep. Paul Broun (R-Ga.). (Courtesy: YouTube)

Rep. Paul Broun has landed the first endorsement from a national tea party group in the crowded Georgia GOP Senate primary, with the nascent Madison Project set to back his candidacy Tuesday.

In its endorsement, which was shared early with Post Politics, the group says Broun has been the House's fiercest conservative, bar none.

"...few come to the ankles of Paul Broun in terms of a proven commitment to constitutional governance," the group will say in a release. "It is not an exaggeration to say that Congressman Paul Broun has sustained the most conservative voting record over the longest period of time of any sitting Republican in Congress. Even the fiercest conservative fighters tend to succumb to the establishment meat grinder after a few years. Paul Broun has been inviolable."

Broun faces a primary with Reps. Phil Gingrey and Jack Kingston as well as former secretary of state Karen Handel and businessman David Perdue, among others. Polling shows the field is crowded.

Other leading conservative groups, including the Club for Growth and the Senate Conservatives Fund, have yet to endorse anyone in the race. Given the crowded primary, it seems quite possible the GOP nominating contest could be headed for a runoff, at which time it might be more tempting for these groups to get involved.

Broun is a favorite of such groups. He ranks fourth among all House Republicans on the conservative Heritage Action's scorecard and first on the Club for Growth's 2012 scorecard.

Democrats have recruited Michelle Nunn, the daughter of former senator Sam Nunn (D-Ga.), for the race, hoping a divisive GOP primary will open the door to victory in a red state.

National GOP groups are indeed wary of Broun, worrying that he could be the kind of candidate that could make the race winnable for Nunn. Some in the GOP establishment have compared him to former congressman Todd Akin, who lost an open Senate race in Missouri in 2012 after saying "legitimate rape" rarely leads to pregnancy.

The Madison Project says the comparison is unfounded.

"The establishment, who views him as the consummate threat of the election cycle, likes to dub him as 'the next Todd Akin,'” the group will say. "'The reality is that Paul Broun has run the most effective and on-message campaign of any of the primary candidates."