Former Rep. Joe Walsh, R-Ill., announced on Sunday that he is running for president, giving President Donald Trump another primary challenger as several other Republicans weigh jumping into the race.

"I'm going to run for president and I'm happy to be on your show announcing my candidacy," Walsh told ABC's George Stephanopoulos on "This Week," adding, "We’ve got a guy in the White House who is unfit, completely unfit to be president. And it stuns me that nobody stepped up. Nobody in the Republican party stepped up."

Walsh claimed "everybody" in the GOP believes Trump is "unfit" for office.

Walsh, a conservative radio host who served one term in Congress, also announced his candidacy on Twitter.

"I’m betting you’re tired of having an unfit con man for a president," Walsh says on his campaign website. "A president who sides with foreign dictators over our intelligence community. A president who spews hate virtually every time he opens his mouth. A president who is teaching millions of American children it’s okay to lie and it’s okay to bully."

"See, Donald Trump doesn’t represent us — he represents the worst of us," Walsh continued. "He hasn’t delivered on his promises, he thinks he’s above the law, and he’s tweeting us into a recession, as we speak. You know it, I know it, we all know it: We can’t afford four more years of Donald Trump. No way."

Walsh joins former Massachusetts Gov. Bill Weld, the Libertarian Party's 2016 vice-presidential nominee, in the Republican primary field facing Trump. Other potential Republican candidates include former South Carolina Gov. and congressman Mark Sanford, former Sen. Jeff Flake of Arizona, and former Ohio Gov. John Kasich.

Weld told NBC's "Meet the Press" on Sunday that he is, "thrilled about Joe Walsh and Mark Sanford" joining the race.

"Again, I've said from the very beginning, I don't think that any of us as challengers will beat President Trump," Sanford, who said he will make up his mind about running around Labor Day, told MSNBC last week, adding, "What has historically happened with primary challengers — though they have not gone on to win the nomination — what they have done in many cases either significantly changed the debate or frankly changed the contours of the election going forward."

Responding to all the possible primary challengers last week, Trump 2020 campaign communications director Tim Murtaugh told NBC News that, "everyone has the right to pursue certain failure."

Walsh, a Tea Partier with a history of incendiary remarks about Muslims and former President Barack Obama, who Walsh had labeled a "traitor," has apologized for some of his commentary. He told "This Week" on Sunday that he doesn't stand by his attacks and false claims about Obama.

"I've apologized for that," he said, noting that "we have a guy in the White House who has never apologized for anything."

Any primary challenger faces a near-impossible climb to defeat Trump, who is both well-financed and enjoys support among Republicans north of 80 percent in many polls.