With just hours to go before Iowa voters go to their caucuses, the final poll from Quinnipiac shows little change in either party. Donald Trump still leads the GOP race with 31%, the same as the Q-poll from the week before, but Ted Cruz has dropped five points to 24%, while Marco Rubio has gained four points to 17%. Bernie Sanders still clings to a three-point edge over Hillary Clinton among Democrats. But the key for both Trump and Sanders still remains how many first-time caucus-goers they can turn out tonight:

Fueled by a big lead among first-time Iowa likely Republican Caucus participants, Donald Trump jumps to a 31 – 24 percent lead over Sen. Ted Cruz of Texas, according to a Quinnipiac University poll released today. Sen. Marco Rubio of Florida has 17 percent, with Dr. Ben Carson at 8 percent and no other candidate above 4 percent. …

Also relying on first-time Iowa likely Democratic Caucus participants, Sen. Bernie Sanders of Vermont has 49 percent, with 46 percent for former Secretary of State Hillary Clinton and 3 percent for former Maryland Gov. Martin O’Malley. Only 2 percent remain undecided and 14 percent of those who name a candidate say they might change their mind.

The key for both Trump and Sanders is first-time caucus goers:

• Trump leads Cruz 40 – 22 percent among these first-timers, while Republicans who attended prior caucuses go 26 percent for Cruz and 25 percent for Trump;
• Sanders tops Clinton 62 – 35 percent among Democratic first-timers, while Clinton leads 52 – 41 percent among voters who attended prior caucuses;
• 44 percent of Republicans and 38 percent of Democrats say this is their first caucus.

One thing can be determined for certain: Iowans will be delighted to stop getting phone calls from pollster after tonight. Bear that in mind as the caucuses approach today, too. There has been a deluge of pollsters on this small population, and there are serious questions being raised about how good their samples have been as people have rejected phone-survey calls at record rates over the last few years.

Assuming that the data’s relatively solid (and Quinnipiac has a pretty good reputation), the next question is turnout. Both Sanders and Trump are riding high on anti-establishment populism and finding new voters to pull into their coalitions more than they are winning the reliable cycle-to-cycle voters. That new-voter engagement will be good news for them (and their parties) assuming they actually turn out to vote. Sanders has spent the money in Iowa to find and motivate these voters to caucus, but Hillary has funded a large ground organization, too. The race is close enough between the two in this poll that Sanders has to squeeze every voter he can find, especially because the drop-off is so dramatic:

Trump’s lead is stronger, but the drop-off is almost as dramatic:

Ann Selzer, who runs the Des Moines Register poll, explains why ground organization matters when it comes to caucusing. She also sees a swell of enthusiasm among younger voters for Sanders, and also among “nones” — those with little or no religious affiliation. Will that also be true on the Republican side? Doubtful, but Selzer’s right about Cruz and Rubio surrogates working the caucuses to get those supporting marginal candidates to throw in with them against Trump. If Trump’s ground game isn’t strong, those same efforts might also sap his own numbers. The Q-poll shows Trump voters with the highest commitment level of the three candidates, but a caucus-night push could change his numbers more if Trump doesn’t have enough organizational strength.

Update: Is Marcomentum real?

Trend of Cruz-Rubio gap in final IA polls:

—Emerson: +9% to +4%
—QPac: +15% to +7%
—DMR: +13% to +8%
—NBC: +15% to +7%
—PPP: +11% to 9%

— Taniel (@Taniel) February 1, 2016

Perhaps, but that may be an argument to watch for a surprise in New Hampshire. One thing’s for sure: A third-place finish in Iowa won’t be bad news for Rubio as long as he’s close enough to the leaders, but a bronze medal would be bad news for Ted Cruz.