Beto O’Rourke had his. Pete Buttigieg is having his. So is Joseph R. Biden Jr. But Jay Inslee hasn’t had his, nor has John Hickenlooper. And when either Kamala Harris or Amy Klobuchar has hers, watch out.

Every four years, a group of presidential candidates have their Moment, a golden intercession when the press and the country discover their virtues, begin to consider them as strong White House contenders and plausible presidents. It happened to Barack Obama in the spring of 2007; he never lost that fairy dust. It happened to Howard Dean of Vermont in late 2003 and early 2004; his magic disappeared by midwinter. It happened to Dick Gephardt of Missouri twice — in late 1987 and again in early 2004; he never caught the campaign wind long enough to cruise to the Democratic presidential nomination.

These men still live with their Moment, the glory that was in their grasp until it migrated to stronger hands able to hold it more firmly, sometimes long enough to propel them to the inaugural platform on the west front of the Capitol.

“Candidates need to translate their Moments into cash,” said Bruce Nesmith, a political scientist at Coe College here and a veteran observer of the first caucus state. “They then need to translate both cash and fame into building organizations, both here in Iowa and around the country.”

The Moment was in the youthful hands of Sen. Gary Hart after he stunned the political establishment by upsetting former Vice President Walter F. Mondale in New Hampshire in late February 1984. Hart had the tail winds because he was new and nimble of mind, and was possessed of a sense of destiny that streamed from his intense eyes and from his possession of “new ideas.” He then streaked through Maine and Vermont, the Mondale mountain wall crumbling like an avalanche.

Then Mr. Mondale’s strategists came up with a gambit for the ages. They looked ahead to Super Tuesday with trepidation, but also with calculation. Mr. Hart, they knew, was positioned to win Massachusetts and Rhode Island by prodigious margins, and to capture Florida, the big prize of the day. All that came to pass.

But the Mondale brain trust began a parallel campaign, not so much for convention delegates as for the conventional wisdom, and they sowed the notion — preposterous on its face, and even more so in the rear-view mirror of history — that Florida and the New England Democratic strongholds counted for nothing, and that the key to political success was the contest in … Georgia.

Georgia was, of course, the home state of Jimmy Carter, the former president who had chosen Mr. Mondale as his running mate in 1976. Mr. Carter was in disrepute in Democratic circles except in Georgia. Mr. Mondale had months earlier gritted his teeth and stopped in Georgia to pay respects to his patron. Political pros at the time wondered about the wisdom of that visit to a onetime president who only later enjoyed historical revisionism by virtue of his post-presidential good works. But it paid off. Mr. Hart won three of the five states contested that day, losing Georgia by only 3 percentage points — but losing the momentum he had cultivated on the ground, though not in the press.

His Moment had vanished, forever. Overall, Mr. Hart won six more states than Mr. Mondale. On the last day of the primary season, he won the biggest prize, California. A day later, Mr. Mondale claimed sufficient delegates to win a nomination that eventually proved to be more dross than dream. But he also proved how fleeting can be the Moment.

Speed ahead four years and there was, as Barbra Streisand sang in an entirely different context, a Moment to remember. It belonged to former Gov. Bruce Babbitt of Arizona, like Mr. Hart a cerebral political figure but lacking the Coloradan’s dash and glamour. Later Mr. Babbitt became secretary of the interior and would have been on the Supreme Court had Western lawmakers not objected to his determination to keep their states free of pollution, and of miners.

The Babbitt Moment crystalized in a late 1987 debate, when he challenged Democrats to confront the budget deficit. Mr. Babbitt proposed a tax on consumption (a “progressive national consumption tax”) and a “universal means test” — no farm subsidies for the rich, new taxes on Social Security for the wealthy.

The press, as always guilty of focusing on politics rather than policy, sought to right its great wrongs and decided Mr. Babbitt was a truth-teller for the times, deeming him a possible hero for the ages.

“These campaign Moments are coveted ‘X factors,’ kind of mysterious … but often fleeting,” Mr. Babbitt said in a conversation the other day, in which he avowed that his Moment came because “people were casting around for a candidate they liked and weren’t finding that in any of us.” When Mr. Babbitt actually said something sensible, at least to Democratic ears, his name was on everyone’s lips.

But not for long. Mr. Babbitt has an unusual sense of self-perception for a politician, and perhaps it is best that he tells of the denouement: “I had deficient communication skills and couldn’t take advantage of my Moment. I couldn’t make my policy proposals morph into a personal connection with voters.”

Mr. Babbitt finished sixth and departed the race.

In years to come, Republicans Ben Carson and Herman Cain would have momentous Moments, with Mr. Cain — he had a cameo reappearance last month as a failed Fed candidate — actually leading the polls in 2011. It was only weeks later that he, too, left the lists.

But not all Moments fade forever. Sen. John McCain had a 2007 Moment, then a 2007 collapse, and then — mirabile dictum — a 2008 revival. He won the GOP nomination, and though he didn’t win the presidency, he went to his death respected by nearly everyone in American life — the principal exception being the current president, whose Moment, perhaps the unlikeliest of them all, has lasted three years.

David M. Shribman is a former executive editor of the Pittsburgh Post-Gazette and a scholar-in-residence at Carnegie Mellon University.

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