Senator Jeff Sessions of Alabama is among the Republican Party figures who have come out in support of Trump. Photograph by Taylor Hill / WireImage

Ever since last Thursday night’s televised G.O.P. debate, the Republican primary race has turned into a demolition derby. Marco Rubio, who for a long time portrayed himself as the young, positive, Kennedyesque candidate in the race, is now calling Donald Trump a “con artist” and throwing every other insult at the front-runner that he can, including, over the weekend, a thinly veiled penis-size joke. Trump, for his part, has been berating “Little Marco” at every opportunity, labelling him a “choke artist” who is too unmanly to be President. Meanwhile, Ted Cruz is attacking both Trump and_ _Rubio.

If you’ve been following all of this bile in real time, on social media, it is easy to miss the larger reality that it reflects. With Trump in a strong position to win the primary, Republicans are engaged in a bitter battle not just about who will represent them in November, but about the broader nature of their party. For the past forty years, the G.O.P. has been an uneasy alliance of social conservatives, free-market conservatives, and corporate interest groups, with the latter largely dictating economic policy. Trump has been drawing on a base of alienated white working-class and middle-class voters, seeking to remake the G.O.P. into a more populist, nativist, avowedly protectionist, and semi-isolationist party that is skeptical of immigration, free trade, and military interventionism.

If he were to succeed in this quest, he would arguably be the most consequential Republican since Ronald Reagan, in part by challenging some aspects of Reagan’s legacy. Of course, Trump’s own bequest could well up being ruinous: if he does get the nomination, his racism, xenophobia, and megalomania would hopefully condemn the G.O.P. to a massive defeat. But even then, the party establishment, in picking up the pieces, would have to deal with the issues and fault lines that his candidacy has exposed.

To transform a political party, you need a clear message, a broad electoral base, and allies within the existing power structure. Trump now has all three of these things. As I’ve pointed out before, his claim that Washington is broken and can only be fixed by an outsider resonates with many Americans, and not just arch-conservatives. So does his demagoguery about illegal immigrants and the supposed threat that Muslims present. What is perhaps more surprising, at least to Washington-based conservatives, is how many Republicans are also embracing Trump’s populist lines on ending free trade, protecting Social Security, and providing basic health care.

Evidently, many ordinary G.O.P. voters are less enthusiastic about Ayn Rand’s view of the world than are corporate-funded politicians and corporate-funded entities such as the Heritage Foundation, the American Enterprise Institute, and the Cato Institute. A similar pattern seems to apply to social issues. Given Trump’s history of support for abortion rights and the fact that he has been married three times, you might think he would be anathema to Christian evangelicals. But Trumpism is sweeping through the Deep South, which suggests that many evangelicals are willing to look past the candidate’s “New York values.”

Having scored large victories in New Hampshire, Nevada, and South Carolina, Trump now looks set to win at least eight of the eleven states that will hold contested Republican votes on Super Tuesday: Alaska, Alabama, Colorado, Georgia, Massachusetts, Oklahoma, Tennessee, Vermont, and Virginia. And he could easily win two more states, Arkansas and Minnesota, that the polls suggest are a bit tighter. The only state that looks to be beyond him is Texas, where surveys show Cruz leading. (Ironically, that could be good news for Trump. If Cruz wins in Texas, he will probably stay in the race, making it harder for anybody to consolidate the non-Trump vote.)

If Trump does as well as expected, it would still be mathematically possible for someone else to emerge as the candidate. But the window of opportunity would be closing fast. During the next two weeks, Republican primaries or caucuses will be held in eight more states—Hawaii, Idaho, Kansas, Kentucky, Louisiana, Maine, Michigan, and Mississippi—plus Puerto Rico and Washington, D.C. In almost all of these places, Trump appears to be leading. (In Michigan, for example, he is twenty points up.) If he comes out ahead in most, or all, of these places, he would be in position to deliver the final blow on March 15th, by coming out on top in the winner-takes-all state of Florida, and in two other delegate-rich states, Illinois (which is also winner-take-all) and North Carolina.

Until recently, Trump’s opponents, and skeptical conservative commentators, consoled themselves with the thought that, despite the enthusiasm of his core supporters, he would struggle to get more than a third of the Republican vote. Now this “low ceiling” theory looks tattered. In Nevada, Trump received almost forty-six per cent of the votes cast. Today, CNN published a national poll showing that forty-nine per cent of Republicans and Republican-leaning independents backed him. (Rubio was in second place, with sixteen per cent of the vote, and Cruz was in third, with fifteen per cent.)

In light of these sorts of numbers, it is hardly surprising that some elected Republicans are starting to hop aboard the Trump bus. Their points of origin are telling. On Friday, Chris Christie, a representative of the Party’s somewhat-less-conservative wing, endorsed Trump. And on Sunday Alabama Senator Jeff Sessions, one of the most influential ultra-conservatives in the Party, did likewise.

Given the fact that Christie was bashing Trump on the stump just a few weeks ago, his endorsement was the most dramatic (and heavily covered) of the two. It indicated that Trump, ultimately, may end up getting the backing of many coastal Republicans and business interests, who aren’t particularly ideological. But in terms of votes in the Republican primaries, and the future direction of the party, it is the Sessions endorsement that probably matters most. A lifelong Republican whom Reagan nominated to a federal judgeship in 1986, his bona fides as a conservative and party loyalist are unquestioned.

“This isn’t a campaign, this is a movement,” Sessions (whose backing Cruz had reportedly been desperately seeking) said to a crowd estimated at about thirty thousand, in Madison, Alabama. He identified immigration and trade as the key issues that had brought him to Trump’s side. “Nobody is perfect,” Sessions went on. “We can’t have everything, can we, Mr. Trump? But I can tell you one thing . . . at this time in American history, we need to make America great again.” With that, Sessions took out one of those red Trump baseball caps—which are stitched together by a Los Angeles firm that employs lots of Mexican immigrants—and put it on, to huge cheers. Heading into Super Tuesday, Trump appears to be unstoppable.