Americans for Prosperity, the Koch-backed Republican group, is again going up with an ad thanking Rep. Steve SoutherlandWilliam (Steve) Steve SoutherlandRules for male candidates MORE (R-Fla.) for his work opposing ObamaCare, another indication of just how tough his reelection fight will be.

The ad declares that Southerland “has it right [on healthcare]— he puts us first, not special interests.” It features clips of Southerland speaking out against the law on the House floor and urges viewers to call the congressman to thank him for his work on the issue.

AFP has previously launched ads to the same effect to boost Southerland. Their efforts reflect the fact that he’s one of the GOP’s most vulnerable incumbents this cycle, and Democrats have a top-tier contender for the seat in Gwen GrahamGwendolyn GrahamFlorida DNC official resigns after 'colored people' remark Florida gubernatorial candidate plans to target anti-Trump Twitter ad toward Mar-a-Lago Florida GOP gubernatorial candidate dips in polls after supporting NRA MORE, the daughter of former Florida Senator Bob Graham.

She released an internal poll earlier this month that showed her statistically tied with Southerland, taking 40 percent to his 42 percent support.