Just what does Joe Walsh think he's doing?

Given that the former one-term Illinois congressman and radio talk-show host just announced he's challenging President Trump for the Republican nomination, you'd think the answer would be obvious. But it really isn't.

The most potent primary challenges to presidents seeking re-election are driven by ideological dissent, as a restive faction of the party holding the White House lashes out in anger and frustration.

Take the two most salient recent examples: Sen. Edward Kennedy's campaign against Jimmy Carter in 1980 and Pat Buchanan's against George H.W. Bush in 1992. Kennedy championed the liberal wing of the Democratic Party that felt underserved by Carter and managed to win nearly 38 percent of the primary vote while carrying 12 states outright. Buchanan rallied the nativist paleocon faction of the GOP and ended up winning 23 percent of the vote. Though Buchanan failed to carry any states, he embarrassed the president by winning 38 percent of the vote in the New Hampshire primary. Both incumbents went on to lose in the general election.

Is this the kind of challenge Walsh is mounting against Trump? Does he speak for an unhappy faction of the GOP's electoral coalition? Given that Trump enjoys the support of roughly 88-90 percent of Republicans, this seems unlikely. (By contrast, Carter's approval among Democrats sank to around 50 percent in the year prior to his contest with Ronald Reagan, while Bush fell below 75 percent approval with Republicans as the 1992 election approached.)

Then there's Walsh's pitch, which, at least so far, seems to position him as … a Trumpist without the defects of Trump himself. Like Trump, Walsh has a long track record of right-wing rabble-rousing (though he's apologized for some of his most egregious outbursts down through the years). Like Trump and many of his supporters, he appears to define himself largely in terms of opposition to the Democratic Party. (Walsh claims to have supported and voted for Trump in November 2016 mainly because “he wasn't Hillary.”) Walsh even seems poised to hit Trump from the right on immigration, claiming that the president has failed to fulfill his campaign promise to build a wall along the southern border.

One might say that Walsh's challenge to Trump is primarily aesthetic or stylistic — just as his recent repudiation of his own inflammatory statements over the years, including declaring on numerous occasions that Barack Obama is a Muslim, seems to be motivated by a concern that his nastiness contributed to Trump's success at demonizing his political enemies.

That's laudable to some extent, as is Walsh's willingness to denounce Trump's lack of temperamental fitness for office and near-constant lying. But is it anywhere near potent enough to viably challenge a sitting president who's quite popular with his own party — especially when all of the defects were obvious before Trump was elected, when the person raising the objections supported him at the time, and when White House staff, Cabinet secretaries, and the courts have repeatedly demonstrated a willingness and capacity to contain the president when necessary?

None of this should be taken to imply that I consider Trump a successful president. Having a president who needs to be contained is really bad and raises all kinds of troubling constitutional issues. Trump spews toxins into our political culture and risks disaster on the world stage nearly every day. It would be very good for him to go down to decisive defeat in 2020, whether or not that outcome is aided by a primary challenge that damages him.

The question is whether Walsh's challenge is likely to advance that cause in a meaningful way — and in a way that will point the way toward a healthier future for the Republican Party after Trump.

In Walsh's statements since announcing his campaign, there are elements of more substantive disagreements with the president — on trade, on the deficit, on the threat posed by Vladimir Putin's Russia. But will Walsh develop them into an alternative ideological vision for the GOP and the country? Or will he prefer to focus on Trump's personal defects?

In this respect, there's greater weight to the primary challenge posed by former Massachusetts Gov. William Weld, who strongly opposes Trump on just about everything, from style to substance, including deep disagreements over trade, foreign policy, immigration, and abortion. Yet Weld's campaign has gone nowhere, showing that there might be little space in the party for divergence from Trumpism. Awareness of this reality may explain why no more prominent figures in the party, including Utah Sen. Mitt Romney, have launched their own primary challenges to Trump.

That leaves us with Joe Walsh — an ostensibly reformed trash-talking talk-radio personality taking on the undisputed king of trash talkers in the Oval Office and betting that the GOP is ready to ditch Trump but keep Trumpism.

That isn't a bet I'd be willing to make.