The solar calendar tells us that, with the winter solstice swiftly receding, the days are getting longer. With the Iowa caucuses scheduled for Monday, the political calendar is getting shorter. 

Shorter for former Gov. Nikki Haley of South Carolina and Gov. Ron DeSantis of Florida to stop the ascendancy of Donald Trump. Shorter for Vivek Ramaswamy to make a move. Shorter for the backers of former Gov. Chris Christie of New Jersey to determine whether they shift their support to Haley in an effort to deny the presidency to Trump.

Big decisions loom, first from the Republicans of Iowa, a famously independent bunch who in this young century alone have given their caucuses to the unlikely Republican trio of former Gov. Mike Huckabee of Arkansas (2008), former Sen. Rick Santorum (2012), and Sen. Ted Cruz of Texas (2016). None came even close to the nomination. All made an impact on the trajectory of the race that continued eight days later in New Hampshire and then turned south and west.

“Iowa takes this responsibility very seriously,” Santorum said in an interview. “They decide late. If Nikki comes in second, then DeSantis is done. But if DeSantis has a strong showing, the whole dynamic could change.”

All the planets of the political solar system revolve, as have all things in American politics since 2015, around Trump. 

The removal of one of those planets would change the orbits of all the other planets, perhaps to the benefit of Haley. The sun’s seasons —  it has them, as Trump does — could produce the political equivalent of a release of a solar stew of nuclei, transforming the political environment. 

“It’s unusual to have a former president campaigning with high ‘name ID’ and many of the advantages of incumbency,” said Brett Barker, Republican chair in Story County, home to Iowa State University in Ames. “But the caucuses will operate the way they always do. Iowans remain really open to the candidates, vetting them, listening to them at multiple locations. The caucuses usually break late, and people are beginning to solidify their choices. But Iowans are still open to hearing from all the candidates.” 

It is not solar flames but prairie fires that Iowa can produce. 

The pioneer youngster Etta May Lacey Crowder, recalling her childhood in Palo Alto County in north central Iowa a century and a half ago (population 4,131 at the time), described a prairie fire as a phenomenon that came “with racehorse speed, for the grass was long and a prairie fire always creates a strong wind.” Sen. Gary Hart triggered just such a conflagration with his surprising second-place in 1984, suddenly becoming the principal rival to former Vice President Walter F. Mondale.    

The smart people say Trump has the whip hand here — high approval ratings, incomparable visibility, fervent supporters, a field wagon of endorsements. Some years that works; some years it doesn’t.

“Endorsements here make candidates happy but don’t mean all that much,” said Steve Scheffler, the Republican national committeeman who is president of the Iowa Faith and Freedom Coalition and is unaffiliated with any candidate.

The smart people also say that Trump is approaching the caucuses in a far different — which is to say, in a far more disciplined — fashion than he did eight years ago, when he was edged out by Cruz. At rallies across the breadth of this state, and in small meetings in rural crossroads, his aides have walked supporters through the intricacies of an Iowa caucus: how to have the most impact, how to cultivate patience in the service of political impact. 

“You have to spend a whole evening there,” said Denise Brubeck, the deputy director of the influential Church Ambassador Network and president of the Capitol Region Republican Women. “You can’t just pop into an Iowa caucus. On the same night, you have to elect our central Republican committee members and our delegates to our district, county and states conventions. There also will be speakers for the candidates before people vote.”

The unknown has real power in the Iowa caucuses. 

Like a late burst of spending.

That’s important in a state where, in pioneer days, a third of Iowa’s total land area was purchased by cash — and where, 24 years ago, a flood of money catapulted publisher Steve Forbes into an Iowa second place. 

Like COVID or a raging cold.

“It’s one thing to get someone signed up,” said former Sen. Tom Harkin, who represented Iowa on Capitol Hill for 40 years. “But on caucus night, sometimes a family gets sick, or the car isn’t running. You never know whether people are going to show up.”

Like the weather.

The weather always is a factor, as it will be Monday. “In bitterly cold weather,” Dorothy Schwieder wrote in her classic 1996 “Iowa: The Middle Land,” “people stayed in bed as much as possible, simply to stay warm.” That represents a particular threat to Trump, though it is unlikely that any of those who are discouraged by the weather will suffer the fate of one man in the 19th century, whose big toe froze because it poked out of the bedclothes.

Like pure exhaustion.

Many agriculture-related innovations — the steel moldboard plow invented by John Deere, for example, or the reapers, mowers, and horse-drawn rakes invented by Cyrus McCormick — were eagerly adopted by Iowa farmers. But, Leland Sage wrote in his “A History of Iowa,” published in 1974, “the improved machinery was a contributor to soil exhaustion rather than improved techniques of farming.”

The cause of modern-day exhaustion that has national implications is the pure fatigue caused by months of town hall meetings, casual candidate encounters on Main Street, meet-the-candidate sessions in Pizza Ranch restaurants, blizzards of television ads, and bursts of social-media entreaties.  

It all will end in a two-hour explosion of political activity. 

Iowans tend to say the soundtrack of their lives comes from the 1957 Broadway show “The Music Man,” written by Meredith Willson, the River City of the production a fictional version of his Mason City, Iowa hometown. 

But in caucus years it is “Brigadoon,” written a decade earlier by Alan Jay Lerner, carrying the threat that once a villager departs, the whole town vanishes. On Monday night, the candidates depart, and the Iowa caucuses vanish.

A Swampscott High School Class of 1972 member, David M. Shribman is the Pulitzer Prize-winning former executive editor of the Pittsburgh Post-Gazette.