Conservative firebrand former Illinois Rep. Joe Walsh announced Sunday with ABC News Chief Anchor George Stephanopoulos on ABC's "This Week" that he's launching a long-shot Republican presidential primary challenge against President Donald Trump.

"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 don't 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," Walsh said.

(MORE: GOP Trump critics moving closer to launching 2020 primary challenges)

While Walsh has argued he plans to make a moral case against the president, Stephanopoulos asked the former congressman if he's the best person to make that argument given his long history of incendiary and controversial statements ranging from using racist slurs on Twitter to promoting falsehoods around former President Barack Obama's birth certificate and religion.

"I helped create Trump," Walsh told Stephanopoulos, "and George, that's not an easy thing to say."

The former Illinois congressman-turned-radio host was once a fervent Trump supporter who's become a fierce critic of the president. Walsh is just the second Republican to jump into the primary behind former Massachusetts Gov. Bill Weld, who announced back in April but has yet to gain serious traction.

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

Walsh has acknowledged there's little chance his candidacy will result in Trump losing the party nomination, and he is instead focused on offering GOP voters an alternative vision for the party.

(MORE: Trump challenger Bill Weld raised just under $700K in long-shot primary bid)

Walsh only served one term in Congress, but his candidacy does perhaps bring a more current figure from conservative circles into the long-shot picture compared to Weld, who last held public office over 20 years ago. Walsh's nationally syndicated radio show and large online following arguably kept him more relevant.

The Trump administration's latest actions around trade and the economy along with what Walsh's team calls an "incredible reaction" and flood of support to an op-ed Walsh published in the New York Times last week is what pushed the conservative radio host to jump into the race.

Walsh's team says he is set to travel to and spend "a lot of time" in the key primary states of Iowa and New Hampshire in the coming weeks.

