"I'm going to run for president," Walsh told Stephanopoulos in an exclusive interview.

When Stephanopoulos pointed out the massive uphill climb Walsh has in front of him in the primary thanks to Trump's overwhelmingly high approval rating within the party, the controversial former congressman argued that conservatives should have an alternative to the president.

"I'm running because he's unfit; somebody needs to step up and there needs to be an alternative. The country is sick of this guy's tantrum -- he's a child," said Walsh, who was elected to the House in the 2010 Tea Party wave, but only served one term before becoming a conservative talk radio host.

Trump campaign communications director Tim Murtaugh sent ABC News a dismissive one-word response to Walsh jumping into the race: "Whatever."