President Trump launched a scathing attack on his Republican challenger, Joe Walsh, before reportedly blocking him on Twitter.

"Can you believe it? I'm at 94% approval in the Republican Party and have Three Stooges running against me. One is "Mr. Appalachian Trail" who was actually in Argentina for bad reasons," he wrote in the tweet.

"Another is a one-time BAD Congressman from Illinois who lost in his second term by a landslide, then failed in radio. The third is a man who couldn't stand up straight while receiving an award. I should be able to take them!" he continued.

The news comes after Walsh confirmed that he would be running against Trump in the Republican primary.

"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," he said on ABC's This Week.

Last week, Walsh, former avid support of Trump's called the President an "unfit divider-in-chief" and said that the Republican Party are eyeing other options.

"If I'm to do it, it's going to happen soon," Walsh told POLITICO earlier this month. "I've been really surprised by the amount of anxiousness from people across the spectrum who want this president to have a challenge because there's just a real concern that he's absolutely unfit."

Walsh responded the Trump's social media block:

“Luckily Trump hasn’t blocked my team (yet) or I wouldn’t have known the madman in the White House is taking shots at me,” Walsh tweeted.

Bill Weld, a former GOP governor of Massachusetts has confirmed that he will run against Trump in the primary. Former Rep. Mark Sanford, R-S.C. recently revealed that he is also considering running against Trump.