Sen. Claire McCaskillClaire McCaskillUnder pressure, Dems hold back Gorsuch support Overnight Defense: General warns State Department cuts would hurt military | Bergdahl lawyers appeal Trump motion | Senators demand action after nude photo scandal The Hill’s Whip List: Where Dems stand on Trump’s Supreme Court nominee MORE (D-Mo.) is going on the air with attack ads against all three of her potential general-election opponents: businessman John Brunner (R), former Missouri state Treasurer Sarah Steelman (R) and Rep. Todd Akin (R-Mo.).

The move is unusual: candidates usually wait until primaries wrap up to attack one opponent, or pick their most likely opponent and focus on attacking them. But while Brunner appears to be the front-runner, it is still a wide open race — and all three have been attacking McCaskill on the air, prompting a response.

"There are three weeks left and it's still anybody's game. We simply can't wait to see who is going to leave middle-class families on the sidelines," McCaskill's campaign said in a statement. "Missourians need to know who is on their side now."

The GOP primary is Aug. 7. McCaskill is a leading primary this cycle and the winner in November could determine control of the Senate next year.

The ads attack Brunner for failing to vote in a number of elections and for nearly bankrupting his family company; accuse Steelman of "pay to play" politics; and hit Akin for wanting to "eliminate the Departments of Education and Energy," "privatize Social Security" and outlaw "many forms of contraception."

McCaskill's campaign said it was a statewide television ad buy but wouldn't discuss whether one candidate was being targeted more than the others — or how much money was behind the ad buy. A Republican tracking the ad buy said it was for $100,000 a small but not insignificant buy in the state.

The Hill rates the race a "toss-up."

This post was updated at 3:15 p.m.