A Rash Leader in a Grave Time Trump could bridge the divide between the elites and GOP voters. Instead, he’s deepening it.

As tribune of the base Donald Trump is successful and inadequate. You see it in the Muslim question. His strength is that he responds to and appears to share the concerns of those who are legitimately worried about whom we allow into the United States—our visa protocols, our vetting, our standards. This is a national-security issue. We have entered the age of ISIS-inspired and ISIS-directed attacks on the West. The latter (Paris) have tended to be bloodier than the former (San Bernardino), because they involve more operatives, more simultaneous targets, more weapons. Whether inspired or directed, the idea of future hits in the U.S.—and everyone, from the most sophisticated desk-jockey intel analyst in Washington to the receptionist at your dentist’s office, will tell you they believe more are coming—is very much on the public mind.

A Paris here would change everything, transposing a detached debate about strategy into a hot and immediate political exigency. There is the real danger events will outstrip sober decision making. The smartest thing I’ve heard the past few weeks was the suggestion that America figure out the most effective and constructive things it could do after a Paris-style attack, and start doing them now. I hope everyone who runs the country is thinking about this. They’d better have a plan.

Republican presidential hopeful Donald Trump

Republican presidential hopeful Donald Trump

But to Mr. Trump. The chairman of the House Homeland Security Committee, Michael McCaul, said Monday that U.S. intelligence officers believe ISIS terrorists are attempting to use the Obama administration’s Syrian refugee program to enter the country themselves: “I believe 2015 will be seen as a watershed year in this long war—the year when our enemies gained an upper hand and when the spread of terror once again awoke the West.” The director of the FBI previously told Congress the U.S. cannot adequately vet the 10,000 Syrians the administration wants to accept.

Under the circumstances public concern is entirely warranted. Good on Mr. Trump for addressing it—and, in addressing it, forcing other candidates to come up with their plans. Bad on Mr. Trump—very bad—for doing it in his usual way. Colorfully, yes—this is a man who knows how to break through the clutter!—but crudely, seemingly off the top of his head, and using his mouth as a blunt instrument. He doesn’t think it through, doesn’t anticipate legitimate pushback, doesn’t try to persuade, only declares. And of course he was confusing and contradictory. We’ll ban all Muslims! Including U.S. citizens returning from an overseas trip? Yes! No! It’s only temporary, a pause. It’s not about religion, it’s about security! He ignores civic and cultural politesse when that politesse is not just old sissy stuff but a melting-pot tradition that exists for good reason. In defense of his stand he evokes FDR’s actions during World War II, which included putting Japanese-Americans in internment camps. Mr. Trump seems to think that was a good thing because FDR did it. But it is regarded as an American embarrassment and a stain on FDR’s legacy. And this is not a Secret of History. Congress officially apologized for internment 27 years ago.

All of this forced us into the nonsensical but at this point compulsive media cycle in which Mr. Trump says something rash, the media pounce, and Republican contenders are told they must denounce him or forfeit their place among the just and the good. Mr. Trump then announces he is misunderstood—that in fact he loves women, Mexicans, Muslims, whoever he has offended this week. Oddly enough, I think he is sincere about this and feels genuinely injured. But one thing an effective leader must always do is know what can be misunderstood and guard against it, what can be misconstrued and used to paint you—and your followers—as bigoted. Leaders try hard not to let that happen. It is the due diligence of politics.

A continuing mystery of Mr. Trump is his failure to impose on himself political discipline. He has been front-runner for six months but he doesn’t act as if he has absorbed the fact that he could become the nominee. At this point he owes it to his country—he owes it to his own ambition!—to become disciplined in terms of statements and policy. It is possible for candidates to be vivid but careful, dramatic but responsible. When you’re winning you can’t just keep pulling it out of your orifices. Mr. Trump’s lack of discipline should worry his supporters. I know it doesn’t, but it should. Because indiscipline shows disrespect. And people pick up on it, they see it.

It is odd too that, as the longtime front-runner, he doesn’t attempt to reassure those who will have some impact on his future, such as state and national party leaders. In his daily actions he could continue to excite his base while subtly signaling to party elders that while he might be an unusual nominee he would, in some recognizable way, be a responsible one. Instead he ties them in knots each day and embarrasses them. That limits his popularity, lowers his ceiling of support, and reinforces the idea he’s an impetuous flake.

He tweets out taunts alerting party stalwarts to his continued popularity in the polls, and noting that while he does not intend to go third-party he certainly could. This is a form of blackmail: Nice little party you’ve got here. Shame if someone blew it up.

GOP leaders seem to be doing the only thing they can—watch the process play out and hope for good outcomes. Sooner or later, they hope, the field will winnow and it will be Mr. Trump with his 35% versus one, two or three non-Trumps who’ll fight over the 65%. Party leaders’ position is delicate. They are certain they cannot win the presidency with Mr. Trump as the candidate. And they know they can’t win the presidency if embittered Trump supporters stay home or bolt. They can’t win with him and can’t win without his people.

Meanwhile Mr. Trump’s supporters, like Mr. Trump himself, appear to care nothing for the GOP. They believe America is in danger and this is no time for party loyalty. In any case they haven’t felt that loyalty for years because the party has disappointed them for years. Mr. Trump is both the expression and a deepening cause of the party’s fissuring.

The biggest reason has been the distance—the chasm—between the party elite at the top, who are more or less for illegal immigration, and the bulk of the party on the ground, who are opposed. In this case there is a chasm between elites concerned that they personally will look bigoted if they take action and voters concerned about who comes into America in the age of ISIS. It is a split, a distance; it is primarily the fault of the top, not the bottom; and Mr. Trump, who through his popularity could choose to be a bridge across the distance is instead functioning as a deepener of it.

If the nominee is not decided in the primaries and everything is fought through at the convention—well, that will be some convention. In the old fashioned, fisticuffs sense.