The problem that candidates like Bush and Kasich face is that it’s not just Trump’s celebrity and outspokenness that are attracting support. Many Republican voters say they like Trump on the issues, as unrealistic as his proposals are. PHOTOGRAPH BY BILL PUGLIANO / GETTY

Oh, to have been a fly on the wall at the headquarters of the Republican National Committee, or at Jeb Bush’s campaign office, when the latest opinion poll from Fox News came in over the weekend. It showed Donald Trump in first place, with twenty-five per cent of likely Republican voters backing him. Ben Carson, the surgeon-turned-politician, was in second place, with twelve per cent. And Ted Cruz, the Texan ultra-conservative, was in third, with ten per cent.

Where were the “serious” G.O.P. candidates? Bush, the establishment favorite, was in fourth place, with nine per cent. Governor Scott Walker, of Wisconsin, who not so long ago was vying with Bush for the lead, was in fifth place, and Mike Huckabee, the former governor of Arkansas, tied in fifth place, with six per cent. Carly Fiorina, the businesswoman, was in seventh place, with five per cent.

These are pitiful numbers, but others did even worse. Senator Marco Rubio, of Florida, and John Kasich, the governor of Ohio, whom many pundits hailed as the victors of the televised debate a couple of weeks ago on Fox News, were locked in a dismal embrace at four per cent. Kentucky senator Rand Paul and Chris Christie, the governor of New Jersey, both got three per cent. Senator Lindsey Graham, of South Carolina, one of the few Republicans to criticize Trump directly, scored zero per cent—yes, zero.

Come on, you might object,that’s just one poll. But it isn’t. On Tuesday, CNN released its latest poll of Republicans and independents who lean Republican, which showed remarkably similar results. Once again, Trump was way ahead of the field, at twenty-four per cent. Bush came in second, at thirteen per cent; Carson was in third, at eight per cent: Walker and Rubio tied for fourth, at seven per cent; Paul was in fifth place, at six per cent.

The establishment candidates, Bush included, fared a bit better in the CNN survey. But when you allow for sampling errors—plus or minus four per cent in the Fox poll, plus or minus 4.5 per cent in the CNN poll—there isn’t much difference in the results. Trump looms over everything, with the other candidates snapping around his ankles. It’s bit like Gulliver and the Lilliputians.

One possible interpretation of these figures is that we are witnessing a temporary phenomenon. At some not-too-distant point, Trump will blow up and the real business of electing a G.O.P. candidate will resume. Having argued along these lines myself a couple of weeks ago, I wouldn’t dismiss the argument, but it needs amending. The longer Trump stays in the race, the more damage he is doing to the Republican Party and its prospects of winning back the White House.

At this stage, he isn’t merely leading in the horse-race polls, which can change rapidly. His overweening presence is driving the G.O.P. toward policy positions, particularly on immigration, that make it virtually unelectable. As Karl Rove and other Republican strategists have realized since the late nineteen-nineties, the party’s future depends on attracting Hispanic voters in such battleground states as Colorado, Florida, and Nevada. Now, Trump is pushing a plan to build a wall along the Mexican border, deport undocumented immigrants, and deprive the children of undocumented parents the right to U.S. citizenship. And other G.O.P. candidates are following his lead.

Ted Cruz has praised Trump for focusing on immigration. On Monday, Scott Walker, said that he, too, would eliminate the automatic right to citizenship for children born to undocumented immigrants. Yet another candidate who is struggling in the polls, Bobby Jindal, the governor of Louisiana, said the same thing on Twitter. About the only Republicans who pushed back publicly against Trump’s immigration proposal were Carly Florina, who said it was “completely unrealistic”; Lindsay Graham, who described it as “gibberish”; and Kasich, who bravely defended the idea of a pathway to citizenship for undocumented immigrants, calling them “a very important part of most of our communities.” Jeb Bush, who also supports a path to citizenship, was conspicuously quiet.

Perhaps that’s not surprising. The problem that candidates like Bush and Kasich face is that it’s not just Trump’s celebrity and outspokenness that are attracting support. Many Republican voters say they like Trump on the issues, as unrealistic as his proposals are. When CNN’s pollsters asked Republicans which candidate could best handle illegal immigration, forty-four per cent of them said Trump. Bush came in second, with just twelve per cent.

Just as alarming for the G.O.P. establishment is the fact that the party’s supporters also ranked Trump highest in handling other important matters. On the economy, he led Bush by forty-five per cent to eight per cent. (Fiorina came in third place, with six per cent.) On handling ISIS, Trump’s lead was a bit smaller, but he still got thirty-two per cent compared to Bush’s sixteen per cent. (Cruz came in third here, with six per cent.)

You didn’t misread the previous paragraph. When asked which candidate in their party could best deal with the threat of Islamist terror, a plurality of Republicans overlooked four sitting senators, three sitting governors, and seven other candidates who in the past have held elected office, in order to opt for a blabbermouth from New York whose foreign-policy and national-security experience consists of hosting golf events in Scotland (where he presumably avoids handshakes so as not to contact germs).

To repeat: it is still early, and no one should underestimate Trump’s capacity to implode. But if his campaign goes on like this for much longer, the G.O.P. could be forced to resort to the same tactic that the Lilliputians used on a visitor who had outstayed his welcome, and put him on trial for treasonous acts. That’s impractical, sure, but Republican leaders would be overwhelmed with delight if Trump, like Gulliver, decided to return from whence he came.