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ST. LOUIS (KTVI)—Over the weekend, Missouri U.S. Senator Josh Hawley weighed into the GOP primary race for candidates who hope to join him in the upper chamber next year, backing U.S. Rep. Vicky Hartzler’s campaign.

“Vicky has the integrity, the heart, and the toughness to represent MO. I can’t wait to work with her,” he shared on social media after making the endorsement during the Missouri GOP’s Lincoln Days events in St. Charles. “I’m so grateful, he is such a champion for our conservative values in Washington and has been such a powerful voice in what Missouri believes in,” Hartzler told FOX2.

It’s the third endorsement from a sitting U.S. Senator, following Nebraska’s Deb Fischer and Iowa’s Joni Ernst.

One of her rivals, U.S. Rep. Billy Long, took to social media Monday taking aim at Hartzler and Missouri Attorney General Eric Schmitt, also in the race.

If Hawley was a big fish in the endorsement race—filing still doesn’t open until February 22–Former President Donald Trump’s backing would still loom large.

Of the Hawley news, New York Times reporter Jonathan Martin said on Twitter, “A big deal on its own, giving Hartzler momentum, but also will echo at Mar a Lago. Trump will be less likely to back Greitens given Hawley’s choice.”

FOX2 political analyst John Hancock echoed the thinking that Hawley’s decision will have some sway with the former President.

Hawley was unlikely to ever land on an endorsement of Greitens, who he called on to resign when Hawley was the state’s attorney general and Greitens was under investigation for ethical and criminal issues that would ultimately push him from office in 2018.

Greitens, who has former Trump advisor Kimberly Guilfoyle on his campaign team, has been vocal about not supporting Mitch McConnell’s bid to become Senate Majority Leader should Republicans re-take the Senate this fall, and a variety of national Republican figures have urged the former President not to endorse Greitens.

“Please don’t. Please don’t endorse Eric Greitens. That’s a nightmare, Mr. President. We’ll lose that seat. But that’s Hugh Hewitt’s opinion, not yours,” the conservative commentator said to Trump in December.

Schmitt scored a December 23 photo opportunity with Trump, and has consistently tangled with the Biden administration in court over issues like border enforcement, which he’s framed as a rollback of the previous administration’s policies.

Prior to the Hawley endorsement, CNN said Trump had yet to find an alternative to Greitens in the race.

“One of the Trump allies who spoke with him about the race said he spoke positively of Missouri Rep. Billy Long and Missouri Attorney General Eric Schmitt during a recent conversation but “wasn’t gushing about either in a way that suggested he plans to endorse,” CNN reported. 

If Trump listens to those urging him not to back Greitens, Hancock said the calculus could lead to either multiple endorsements of other candidates or no endorsement at all.