A PSA for readers who’ll spend the day hearing talking heads babbling about expected turnout. By now, anyone following the race in Iowa knows the basic dynamic: High turnout favors Trump, as it likely means he’s convinced thousands of disaffected Iowa voters to register as GOPers tonight and caucus for him. Lower turnout favors Cruz, as Cruz by wide acclaim has the best organization in the state. Cruz fans will show up, thanks to Cruz’s superb GOTV operation. The mystery is whether Trump fans will. If you believe Cruz’s campaign manager, the nerds on Team Cruz have calculated precisely how many likely caucusgoers were still trying to decide between him and Trump this weekend: 9,131, with another 6,000 voters total trying to choose between Cruz and Ben Carson and Cruz and Marco Rubio. What Team Cruz doesn’t know is how many newbies will show up for Trump. That’s where turnout comes in.

“High” and “low” don’t tell you much, though. What’s the actual number that will tell us if things are breaking Trump’s way, with new waves of voters coming out, or Cruz’s way? Per Tim Alberta, it’s 135,000.

Officials from many of the campaigns predict the number will fall somewhere between 125,000 and 140,000. A few even think the figure could remain relatively static at 122,000, arguing that Ron Paul drew many first-time caucus-goers in 2012 who won’t be back this time.

“With all these candidates, all this turnout effort, it’s logical that we’ll have a record turnout. But it’s illogical to think we’ll double the record turnout or that it’s going to go to 170,000,” says Iowa representative Steve King, a Cruz supporter. “I think Cruz wins this in a close race, with a 135,000 turnout number as the over/under, and I think we go under that.”

The Cruz campaign has done extensive modeling on the caucuses and believes the turnout will ultimately fall between 133,000 and 137,000. Republicans familiar with Cruz’s analytics program say his team has modeled caucus electorates all the way up to 175,000 out of an abundance of caution, and feels confident that its man will prevail even if turnout reaches that high. The reason: Cruz will hold a lead of roughly 7,000 votes over Trump with a GOP electorate of 125,000, his allies say. Trump would need to win a huge plurality — if not a majority — of additional votes in order to offset Cruz’s lead.

The record for Republican turnout is 122,000, set four years ago. Democrats doubled that total in 2008 during Obamamania, but Obama had what was probably the best organization in political history and plenty of early warning that turnout would be off the charts based on the number of new Democratic registrants before the caucuses. New Republican registrants are up this year too, but not by much. That’s the challenge for Trump tonight. If he’s going to pull this off, he’ll need to either bring out droves of voters who are already registered Republican but have never bothered to caucus before and/or he’ll need to blow the doors off with unprecedented same-day registration by Democrats and independents. But then, that’s a microcosm of the whole race: The only way Trump wins is by doing things that conventional politicians are unable to do. No problem for him on that score so far, but tonight’s the acid test.

To give you a sense of just how organized Team Cruz is:

“Our voters tend to be voters who vote consistently,” Mr. English said. The campaign worked from lists of past caucus participants, then built profiles on individual voters based on what the voters relayed as their overriding areas of interest.

It is a sophisticated, narrowly tailored approach: Borrowing from the latest research in behavioral psychology, the campaign gave its precinct captains talking points from which to write personal notes or to make calls telling supporters that the captains were looking forward to seeing them on Monday…

“I’ve seen no evidence of and heard no supporting evidence to suggest [Team Trump is] running anything like this,” Mr. English said, nodding toward the din of dozens of simultaneous phone conversations [at Cruz’s phone bank]. “If this is what it takes to get regular caucus voters to go to caucus, it would take this plus something in order to get people who don’t.”

Cruz is relying on lots of personal contact with individual voters to build a bond that’ll get them to show up tonight. Trump is relying on the force of his own personality, amplified many times by saturation media coverage, to build the same bond. Under the traditional laws of politics, a Cruz-style bond is worth much more than a Trump-style. Funny thing, though: The traditional laws of politics haven’t worked for the past eight months. Trump’s support is tremendously loyal too, as anyone who’s interacted with a Trump fan online knows. The most eye-popping number from this weekend’s Selzer poll was his favorable rating — a measly 50/47 compared to 70/21 for Marco Rubio and 65/28 for Cruz. Normally, a candidate who’s barely above water within his own party would be an also-ran in an election. Not Trump. The same poll found him leading Cruz by five points. Most of the 50 percent who view him favorably view him very favorably. He’s built the bond, even at a remove.

Here’s Trump’s daughter Ivanka showing Iowans how to caucus. Earlier forecasts suggested a blizzard would hit tonight, suppressing turnout and helping Cruz, but the latest projections is that it’ll arrive in state a few hours after the caucuses end. By the way: According to the Hill, “GOP strategists expect between 150,000 and 185,000 voters will turn out” for tonight’s GOP election. Even Team Cruz admits they’re in the trouble if we veer towards the higher end of that estimate.