Senate Majority Leader Mitch McConnell faces his highest-profile challenge yet, with former Marine fighter pilot Amy McGrath announcing she'll seek to unseat the Kentucky Republican next year in what is sure to be an expensive campaign.

McGrath, who raised millions in an unsuccessful effort to win a House seat last year, said McConnell "bit by bit, year by year, turned Washington into something we all despise."

"I'm running for Senate because it shouldn't be like this," she said in an announcement video.

McGrath was the Democratic nominee against Republican Rep. Andy Barr in 2018, losing 51 percent to 48 percent in a district President Donald Trump won 55 percent to 39 percent in 2016. McConnell was re-elected with 56 percent of votes in 2014 against Democrat Alison Lundergan Grimes, who got 41 percent.

Trump won the state by 30 points in 2016 and he remains popular there, but polls have shown McConnell to be much less popular. McGrath focused her fire in her three-minute announcement video on McConnell, not Trump.