It may not be saying too much that derails Donald Trump, but saying too little.

As amply demonstrated at the GOP debate Wednesday night, the blustering front-runner in the Republican nomination race is an unequaled expert about himself but shockingly shallow on most issues, especially foreign policy, where his simplistic and usually wrong-headed responses belie today’s’s geopolitical complexity.

In just one example, Trump’s parochialism again surfaced when he fielded a question about his knowledge of the Mideast by referring to a list that had “Arab name, Arab name,” and then claiming that “there are few people anywhere who would have known those names.”

Actually, many recognize the names of key Arab allies and adversaries and know what makes them tick. But none of those experts seems to be advising Trump. And the candidate himself seems disinterested in learning even baseline information about the Middle East, or any other key region. This lack of curiosity and rigor from the ill-tempered celebrity-turned-politician is yet another reason for Republicans to quickly coalesce around better-qualified alternatives.

One may be another outsider, Carly Fiorina, who established credibility Wednesday just as she had in August’s debate among lower-polling candidates. Low poll numbers may not characterize Fiorina much longer. Beyond showing substance, she was among the most willing to call out Trump’s errors and flaws, not least his misogyny.

Soft-spoken Ben Carson, meanwhile, another unconventional hopeful, had just the opportunity the doctor ordered when asked to set the record straight about vaccines. An unmistakable message about their efficacy and safety would have been welcome from the pediatric neurosurgeon. Instead, his equivocal answer disappointed, as did his lack of specifics on other policy matters. Carson will likely remain well-respected and well-liked. But, like Trump, he remains unimpressive on the issues.

Ohio Gov. John Kasich, conversely, made a compelling case as to why his congressional and gubernatorial experience would be an asset in working within Washington and in world capitals. He drew a clear contrast with many of his rivals in his support for multilateral diplomacy. On Iran, like rivals, he disapproves of the deal. But Kasich’s caution about fraying Atlantic alliances by ripping up the deal on Day One, as some pledge to do, suggests a more mature and effective approach to global affairs.

Rand Paul also found his voice when warning against more war. Too many others, including Fiorina, were more bellicose and seemed to dangerously discount the value of diplomacy, forgetting that even Ronald Reagan (whose museum hosted the debate) negotiated with adversaries.

A number of candidates had their moments, including Jeb Bush, who logged his best showing so far. And Chris Christie rightly declared the race is about the voters, not the candidates.

It would be best if those voters quickly culled the vanity candidates and more extreme ideologues from those willing and better able to work within an international system, as well as a Washington likely to remain riven by divisions. And it shouldn’t take another three-hour-debate to identify the difference.