Vermont Sen. Bernie Sanders and New York Rep. Alexandria Ocasio-Cortez endorsed Democratic Kentucky Senate candidate Charles Booker on Tuesday, breaking with the party’s senatorial committee on the best choice to challenge Senate Majority Leader Mitch McConnell.

Booker, a state representative who supports “Medicare for All,” is battling Marine veteran Amy McGrath and eight other Democrats in the June 23 primary. McGrath, who had $14.8 million in her campaign account on March 31, has the support of the Democratic Senatorial Campaign Committee.

“Charles Booker is running for Senate & building the kind of principled, inclusive, and winning coalition in Kentucky that can inspire positive change,” Ocasio-Cortez wrote on Twitter. “The US Senate will be a better place with him in it. I’m proud to endorse him.”

The tweet linked to a fundraising page, which could be the chief value of the endorsement if liberal donors around the country send money to Booker. As of March 31, he had just $70,000 in his campaign account.

Booker released an ad this week saying that Kentucky “needs a real Democrat” and accusing McGrath of being a “pro-Trump Democrat.”

Booker, who is black, has also gained prominence in recent days for participating in social justice protests.

McGrath was the beneficiary of a grassroots fundraising surge two years ago when she raised $8.6 million for an unsuccessful challenge to Republican Rep. Andy Barr in the Lexington-based 6th District. Barr, who raised $5.3 million, won by 3 points.

In her Senate campaign, McGrath stumbled after announcing her bid. First, in her launch video, she spoke of writing letters to lawmakers and getting no response, with an implication that McConnell never responded. But then it appeared the letters were sent the same day that she announced bid to challenge him.

She also reversed course on her position on the nomination of Brett M. Kavanaugh to the Supreme Court.

McConnell had just under $15 million in the bank on March 31. Inside Elections with Nathan L. Gonzales rates the Kentucky Senate race Solid Republican.

Kate Ackley contributed to this report.