TRENTON -- One in four Donald Trump supporters in Iowa failed to show up to the state's presidential caucuses last week to cast ballots for him, a new Montclair University poll has found.

Every election will have some voters who don't go to the polls for one reason or another. But Patrick Murray, the director of the Monmouth University Polling Institute, said the fall-off in support for Trump was especially noteworthy because it was enough to give U.S. Sen. Ted Cruz of Texas a victory in the Republican caucus, the first nominating contest in the presidential race.

A pre-Iowa caucus poll had Trump with a 7-point lead from Jan. 23 through Jan. 26, with with 30 percent support for the real estate tycoon, and 23 percent backing Cruz.

Monmouth found that among those who initially supported Trump, 24 percent decided to stay home on caucus night -- far more than the number of initial Cruz and Rubio (both 13 percent) supporters who did not participate.

More murky is why Trump's supporters bailed out.

"One issue is that they are not regular caucus voters," Murray said. "We knew that the Trump voters were disproportionately drawn from people who don't participate in these kind of events. It's not something ingrained into them as their civic duty."

But Murray said there were several other reasons given by the panelists interviewed.

"For some of them, the initial thrill had gone," Murray said, while others pointed to the fact that Trump "didn't show up in Iowa" for the seventh GOP debate, opting to hold his own event instead. And the narrow window of time during which Iowans can caucus -- 6 p.m. to 8 p.m. , could have been a factor, too.

In all cases, the sub-sample was just "way too small to put a percentage on it with any statistical reliability."

Regardless of what caused them to vanish, Murray says he thinks the differential to be large enough such that "we may see a falloff in people who say they are for Trump right now but wind up staying home" when the New Hampshire primary is held on Feb. 9.

Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @ClaudeBrodesser. Find NJ.com Politics on Facebook.