Rick Santorum’s win in the Louisiana primary told us a lot of things we already knew about Mitt Romney’s problems — in very stark terms.

But it might be the last time that happens.

Early exit polls Saturday night showed Romney losing by near-double digits overall. But it also showed him losing basically every demographic group in the state, with one notable exception: voters making more than $200,000 per year.

View Photo Gallery: The Republican hopefuls continue their pursuit of the presidential nomination.

Louisiana might be the most conservative GOP primary state to have voted so far. Exit polls showed nearly half of voters identified themselves as “very conservative” — on par with the most conservative state to vote so far, Oklahoma.

Romney also lost some demographics where he has usually beaten Santorum, including among Catholic voters and those who described themselves as moderates or liberals. Even among voters who did not identify themselves as either Catholic or evangelical, Santorum won handily.

At the same time, this is likely one of the last times Romney will face such a difficult electorate.

Louisiana is the last state from the Deep South that will vote, bringing an end to what has been Romney’s most difficult region of the country.

Next month’s contests will take place almost totally in the Northeast — a region where Romney is thus far undefeated.

In addition, a few of those states award their delegates on a winner-take-all basis — something only two states have done so far — allowing Romney to expand his delegate lead more quickly than he has to this point.

He leads by about 300 delegates overall, and that won’t change much based on Saturday’s results, because only 20 of Louisiana’s 46 delegates were at stake, and they will likely be split between Santorum and Romney.

Santorum may get a little momentum off his win — as the media continue to question Romney’s appeal to conservatives — but Louisiana is one of the last states that will put a magnifying glass on that problem.