Charles Rex Arbogast / AP

The Trump treadmill was turned on high during the Republican front-runner’s blustery appearance at a CNN town hall in Milwaukee Tuesday night.

It’s a dynamic that has shaped support for Donald Trump throughout his turbulent rise in the Republican presidential race. A key to Trump’s hold on his constituency is his willingness to say things in public—about groups from undocumented Mexican immigrants to Muslims to women—that others would not say and then to defiantly double-down when criticized. That combative, unflinching talk has helped him convince his heavily working-class coalition both that he’s not a typical politician, and that he will fight by whatever means necessary to reverse the economic and cultural trends that they believe are marginalizing them. But the serrated language and brusque behavior that electrifies his supporters has reinforced doubts about Trump among Republicans outside of his coalition, and especially in the broader voter pool waiting in the general election. This is the Trump treadmill: The faster he runs to solidify his hold on his supporters, the harder it becomes to gain any ground with other voters. For all of his furious activity, he is largely running in place, with any gains among the groups most receptive to him offset—or exceeded—by losses among those most skeptical.

The Trump treadmill helps explain why opposition to Trump, as the primaries proceed, is deepening, and not dissolving. It seems like a lifetime ago, but in late January thoughtful senior Republicans started to hint the party could live with Trump as a standard-bearer. Bob Dole, the centrist former GOP presidential nominee, told the New York Times he believed Trump would be a stronger general election candidate than Ted Cruz, who Dole said would precipitate “cataclysmic” Republican losses down the ballot. Trump seemed to make such consolidation inevitable by dominating the race’s early stages through Super Tuesday on March 1.

Trump still has a better chance than anyone else to win the GOP nomination. But in retrospect it’s clear his candidacy reached a turning point when he stepped back on the Trump treadmill on February 28. That was the day Trump, in an interview with CNN’s Jake Tapper, repeatedly refused to condemn former Ku Klux Klan leader David Duke or to denounce the organization itself. Trump later blamed his response on a faulty earpiece and disavowed Duke a few days later. But Trump’s refusal to forthrightly condemn Duke or the KKK on national television two days before a big concentration of Southern states were due to vote on March 1 seemed too clever by half—and sent alarm bells ringing through the party.

In the minuet over Duke, Trump had again signaled to his ardent supporters his “toughness” and freedom from “political correctness.” But the encounter also halted any movement toward Trump among mainstream Republican leaders. As veteran Republican strategist John Brabender has noted, Trump’s sweeping Super Tuesday victories offered the New Yorker another opportunity to convince GOP leaders that they could safely entrust the party’s fate to him this fall. Instead, in his own version of March madness, he has repeatedly bounded back on the Trump treadmill for a succession of confrontations ranging from his defense of an elderly white man who sucker punched a black protester at one of his rallies (March 9); to his refusal to accept any responsibility for the edgy atmosphere of violence at his rallies that culminated in a near-riot in Chicago (March 11); to his twitter war against Ted Cruz and his wife Heidi (March 22).

Trump’s unreserved defense this week of his campaign manager Corey Lewandowski, after he was charged with battery against a female reporter, continues this pattern. Both in the CNN town hall Tuesday, and a Today show appearance Wednesday, Trump praised Lewandowski, belittled the reporter, and even suggested he might pursue legal action against her. Amid that torrent of words, the one thing Trump did not say in either interview was that he believed it was categorically wrong for a man to use physical force against a woman. Such an omission may help explain why Trump’s unfavorable rating among all women registered voters reached a stratospheric 73 percent in the latest CNN/ORC national poll.

It’s instincts (and general-election poll numbers) like those that leave Trump facing intensifying resistance from GOP leaders—at a point when previous candidates in his front-runner position have seen the party coalesce behind them. Trump has largely plateaued with voters, too, reaching a ceiling of around 40 percent backing in almost all contests at a time when earlier front-runners were moving toward majority support. (At a comparable point in 2008 McCain hit 50 percent or more in eleven consecutive contests; Trump has not won half the vote in any of the 31 states that have voted and has reached at least 45 percent in only five.) Exit polls show Trump consistently drawing less support in the GOP primaries from women and college graduates than from men and non-college educated Republicans; in the national CNN poll, nearly two-thirds of the Republicans not supporting Trump said they viewed him unfavorably.

Trump is still the clear leader in the race, but he remains only a plurality front-runner. Next Tuesday’s primary in Wisconsin—a state Trump should win with its large blue-collar and relatively smaller evangelical Christian populations—will provide a revealing signal about whether his insatiable appetite for confrontation is increasing or eroding the number of Republicans willing to ride the Trump treadmill all the way through November.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.