The Missouri primary is the only so-called “beauty contest” in the Republican presidential race this year.

But it might be remembered as where things got a little ugly for Mitt Romney.

Republican presidential candidate and former senator Rick Santorum poses with supporters after speaking at a campaign rally Tuesday in Blaine, Minn. Despite a strong showing in that state’s caucuses, the Missouri primary was his biggest win Tuesday. (Photo by Ben Garvin/Getty Images)

With big wins in Missouri and Minnesota — two of the three states holding contests Tuesday — Santorum has cast at least some doubt on Romney’s presumptive nominee status for the entire three-week lull period before another state casts its votes.

And Missouri, despite being the most inconsequential race of the day when it comes to the GOP delegate race, may actually have been the most important to the narrative going forward.

The reason: Missouri is a confluence of odd circumstances that all seemed to play into Santorum’s hands.

First, the state legislature failed to move a Feb. 7 primary date that violates Republican party rules that prohibit most states from holding primaries before March. Instead, the party set a caucus for March and, to avoid being penalized, made it so Tuesday’s primary had no bearing on the state’s delegates.

Then, Newt Gingrich didn’t qualify for the ballot.

We didn’t know it at the time, but this created a near-perfect setup for Santorum in the current four-way matchup.

Gingrich didn’t compete because he couldn’t, Ron Paul didn’t compete in the state because there were no delegates at stake (he’s got a delegate-focused strategy), and Romney didn’t compete in the state because it was supposed to be pointless.

But Santorum didn’t see it that way. In fact, he saw it as a great way to make a point.

Given his win in the neighboring Iowa caucuses, his strength with Midwestern voters, the low turnout that was expected Tuesday, and the fact that Romney invested basically nothing in the state, it fell to Santorum to pull out a victory to prove he can beat Romney head-to-head.

Romney’s campaign did a good job of setting expectations in the runup to its loss in Missouri and the other states Tuesday, noting that there were no delegates at stake in Missouri and the caucus in Minnesota doesn’t directly lead to delegate allocation either. Because of this, many reporters and analysts declared before Tuesday’s elections that they were effectively meaningless.

That’s an entirely fair argument. After all, if Romney were to have mobilized his full campaign in Missouri, we likely would have seen a far different outcome. But he didn’t.

Thus, his campaign has a headache on its hands — especially given that he lost by 30 full points in Missouri and close to that amount in Minnesota.

At this point in the presidential race, it’s about expectations and momentum. And the perceptions of both have changed post-Missouri at least somewhat.

By winning in Missouri, Santorum proved three things:

1) That Romney can lose

2) That he can beat Romney head-to-head under the right set of circumstances

3) That this race isn’t yet over

Santorum is not a front-runner yet; that’s still clearly Romney. But the former Pennsylvania senator did do something to call into question Romney’s coronation.

On Wednesday morning, there will be a bigger sliver of doubt about that coronation than there was on Tuesday morning. And Santorum, rather than Gingrich, will at least momentarily take the role of the guy who can fill the void.

Even if he didn’t win any delegates on Tuesday, that’s a victory nonetheless.