Clockwise: Former Secretary of State Hillary Clinton, Sen. Ted Cruz, and Sen. Bernie Sanders  (Lucian Perkins for The Washington Post)

After Ted Cruz’s victory in Iowa on Monday, election observers are already spinning theories about how he won from “data scientists,” to a better ground game to Trump’s decision to skip the debate on Sunday.

Some of these theories are plausible, but another factor deserves emphasis: strongly ideological candidates perform better in caucuses because caucus electorates are quite different, even than primary electorates. As we have emphasized before, caucuses attract not only a smaller group of participants (even when turnout beats expectations, as it did last night), but also a more ideologically committed group.

Americans are not a terribly ideologically polarized group of people — even those who vote in primaries. But caucus-goers are a different story. They are consistently ideological and more likely to support conservative or liberal candidates as opposed to moderates.

So although the tactics of each candidate can matter, the campaign plays out on political terrain that is shaped by more fundamental forces, including electoral institutions. Cruz, who bills himself as the consistent conservative in the race, was competing on very friendly electoral turf in Iowa.

Besides Cruz, Bernie Sanders — the more liberal Democratic Party candidate — also beat expectations, prompting Matthew Yglesias to suggest that Democrats need a wake-up call. Perhaps.

But Democrats may just want to wait and see how things unfold in the coming weeks.  The upcoming primaries in New Hampshire, South Carolina and elsewhere will present a different challenge for both Cruz and Sanders — even if Sanders has a sort of home field advantage in New Hampshire.  On the whole, the more moderate and more representative electorates that participate in primaries will help a different set of candidates.

Still, this difference between primaries and caucuses is likely to continue to matter, as the battle between Hillary Clinton and Barack Obama showed in 2008. That year, Obama’s narrow margin of victory could be traced to his superior performance in caucus states.

Looking forward, Cruz and Sanders are likely to do better in caucus states like Nevada (February 23), Alaska (March 1), Kansas, Kentucky and Maine (all on March 5) than in the primary elections held in most other states. But there just aren’t enough caucuses for candidates like Cruz and Sanders to win.

That’s why it makes sense that Marco Rubio’s chances of winning the nomination jumped dramatically after his unexpectedly strong showing in Iowa — far more than did Cruz’s chances. And it’s why, despite her “virtual tie” against Sanders, Hillary Clinton’s chances of the nomination are basically unchanged.

Christopher Karpowitz and Jeremy C. Pope are political scientists at Brigham Young University.