Herschel Walker, a former University of Georgia football great, has filed to run for the U.S. Senate in Georgia, becoming the most notable Republican to face incumbent Senator Raphael Warnock (D-Ga.).

Walker had been expected to run, and he has switched his voter registration from Texas to Georgia, where he was a standout running back from 1980 to 1982.

Former President Donald Trump urged him to run, saying, “Run, Herschel, run!” and predicted that he would be just as “unstoppable” as a candidate as he was during his football career, Daily Caller reported.

Walker filed with the Federal Election Commission on Tuesday, Aug. 24, according to the Atlanta Journal-Constitution. Within days, he is anticipated to make a public declaration announcing his candidacy.

However, several state Republicans are concerned that Walker, as a political outsider, may not be prepared or capable of defeating Warnock, the nation’s top fundraiser. According to a recent FEC filing, Warnock has raised more than $34 million and has a solid war chest of $10.5 million cash on hand.

The Democratic pastor from Atlanta has gained a national reputation as a supporter of progressive electoral changes, which has boosted his popularity on the left. In the 2018 midterm elections, he will be a prominent target for Republicans and a key priority for Democrats to defend.

Walker, 59, will be well-known in Georgia as a Heisman Trophy winner and outstanding running back for the Georgia Bulldogs and a 12-year NFL career. However, according to The Blaze, his lack of political experience and unknown policy opinions are causing some state conservatives to worry.

Walker’s Republican primary opponents and Democratic opposition researchers will also make his mental condition a point of contention. Walker has been outspoken about his fight with dissociative identity disorder, writing in his 2008 book “Breaking Free: My Life With Dissociative Identity Disorder” on how the illness impacted his personal life and contributed to suicidal thoughts.

A recent Associated Press investigation into Walker’s past uncovered previously undisclosed public records about his business operations and divorce from ex-wife Cindy Grossman.

“The documents detail accusations that Walker repeatedly threatened his ex-wife’s life, exaggerated claims of financial success, and alarmed business associates with unpredictable behavior,” the AP reported.

Walker is already being pursued by at least one key foe. In early August, Agriculture Commissioner Gary Black ran an ad portraying Walker as a carpetbagger. 

In a statement, he said that if Walker wants to run for Senate, he should “Move here, pay taxes here, register and vote in some elections and learn what Georgians have on their minds.”

According to the Washington Examiner, Walker has not voted in an election since 2003, including the 2016 presidential election.

Kelvin King, a black Trump surrogate, and Latham Saddler, a former Navy SEAL and Trump administration official, are also running in the Republican primary on May 24, 2022.