Movie star Michael Douglas is throwing his support behind Rep. Bruce BraleyBruce Lowell BraleyOPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer MORE (D-Iowa), who is in a tight race

to win the seat of retiring Sen. Tom Harkin (D-Iowa).

“[Braley] is a staunch progressive who’s done great work in the House of Representatives as a champion of the middle class, veterans, and others who need a strong advocate in Congress,” Douglas said in a campaign statement Saturday.

“Now, in his first run for Senate, he's facing a Tea Party Republican who wants to repeal the federal minimum wage, privatize Social Security, and transform Medicare into a voucher program,” he added.

Braley is running against Republican state Sen. Joni Ernst, a Tea Party favorite. Recent polls put Braley at a 44 percent lead against Ernst, who edges closely behind with 40 percent.

The race is key to Republicans who want to take back the Senate this November.

Douglas warned if Republicans win the Senate, they will “kill the New START treaty, torpedo negotiations with Iran, and ramp up nuclear spending to Cold War levels and beyond.”

He also accused the Koch brothers of using their financial clout to help secure the seat for Republicans.

Americans for Prosperity, a political action committee funded by the Koch brothers, have already pledged $125 million into the race and have begun airing ads against Braley.