Joe Walsh is not only slamming President Trump, he’s saving some of his firepower for one of his fellow long-shot GOP presidential primary challengers.

Taking aim at former South Carolina governor and congressman Mark Sanford, the former one-term congressman-turned-conservative-radio-host charged in an interview with Fox News that Sanford is “not serious.”

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Sanford has repeatedly emphasized that he launched his uphill presidential campaign to spark a conversation about the skyrocketing federal deficits and the national debt, while acknowledging that defeating the incumbent president in the GOP primaries is nearly impossible.

That doesn’t sit well with Walsh, who said that idea is “silly” and that “I’m in this to win. This is a pain in the ass. I’ve been this for a month. This is the most difficult thing I’ve ever done. I’m not in it to start a conversation about the debt.”

Last month Sanford told Fox News he would vote for the president next year if Trump wins the GOP nomination and a progressive candidate captures the Democratic nomination.

“I’m going to vote conservative and I’m going to vote for the conservative choice,” he explained.

Walsh, of Illinois, again targeted Sanford, saying if “Trump is the eventual nominee, Sanford’s going to vote for him. That’s like crazy. Trump’s unfit. He’s a danger to the country. Sanford’s not serious.”

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Asked about the criticism from Walsh, Sanford told Fox News on Thursday that "I can’t imagine anything more serious that debt and deficit and government spending."

And he emphasized that "issues are the bedrock to what political change and debate and elections are all about. I’m talking about real issues and will continue to do so."

Walsh spoke with Fox News after arriving in the first-in-the-nation primary state of New Hampshire on Tuesday, two days after he and Sanford battled over the Trump impeachment inquiry during a joint appearance Sunday on CNN.

While Sanford’s not sold on the House Democrats' impeachment inquiry over the Ukrainian controversy that’s threatening Trump’s presidency, Walsh doesn’t have any qualms.

“Look, he’s going to be impeached. He should be impeached. He’s going to be a disaster if he’s at the top of our ticket next year,” Walsh charged.

Trump’s under fire over his July 25 call with Ukrainian President Volodymyr Zelensky, in which he urged Zelensky to investigate former Vice President Joe Biden and his son Hunter over their dealings in the eastern European country that’s been battling Russia. Fueled by whistleblower complaints and a transcript of the call released by the White House, Democrats argue the president was asking a foreign country to potentially interfere in a U.S. election.

Trump has repeatedly insisted that he did nothing wrong and has on numerous occasions described his conversation with the Ukrainian leader as “perfect.”

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Walsh charged that “Trump’s a traitor. When you invite and or pressure a foreign government to screw around with our elections, that’s a betrayal of this country. Trump’s done that from the moment he got elected. He’s probably the most disloyal president this country’s ever had.”

Polling indicates the president remains extremely popular among Republicans and crushes his GOP challenges in the latest primary surveys.

But Walsh insists Trump’s “support is soft.”

Pointing to Republicans he’s talked to on the campaign trail who support a primary challenge to the president, Walsh said, “Almost everyone said ‘Yeah, I’m sick of it. Yeah, I’m exhausted with him, but what else am I going to do.’ I hear that over and over.

“I think that the vast majority of Republicans don’t want four more years of this president’s bulls--t. I just don’t think they do,” he insisted.

Walsh arrived in the Granite State as the third Trump primary challenger, former Massachusetts Gov. Bill Weld, was campaigning in the state. Weld is targeting independents, who can vote in New Hampshire’s GOP primary as well as contests in nearly two dozen other states.

“I got a different strategy. I’m going right at Republican voters,” Walsh explained.

And he predicted that “it will work itself out...Bill Weld’s a great guy. He seems to be focused on New Hampshire. I don’t think Mark Sanford is serious at all. I don’t know how long he’ll be around. I think this race will coalesce around one alternative to Trump.”

Walsh has baggage of his own. After jumping into the race this summer, he apologized for past racist comments on Twitter.

“There have been times over the last six or seven years when I went over my skies and said things that I regretted,” he noted. “I’ve apologized for helping to create Trump, for helping to create the toxic environment that helped to create Trump. Look, I was part of that Tea Party wave in 2010. I went to DC to raise hell about all of this debt and the bankrupting of the country by both parties.”