Rick Santorum is likely to win the Louisiana Republican primary on Saturday. He has had a clear and fairly consistent lead of about 14 percentage points in recent polls there.

Moreover, Lousiana’s demographics are favorable to Mr. Santorum and it is the sort of state where Mr. Santorum has overperformed his polls. And Mr. Santorum has more wiggle room than in past Southern states since Newt Gingrich’s standing seems to be diminished; Mr. Gingrich, instead, is tracking to only about 19 percent in the polls.

While I always urge caution against treating an election outcome as being certain — especially when it comes to voting in the Deep South — there is just not a lot of reason to expect an upset by Mr. Gingrich or by Mitt Romney, who is running second in the polls.

A win in Louisiana, however, would make only a fairly marginal difference in the delegate count. Although the state has 46 delegates, only 20 of those delegates are awarded based on the primary outcome (the rest are awarded at the state convention in June).

The delegate allocation is proportional, moreover, among candidates who reach a 25 percent threshold of the statewide vote. Candidates who do not reach the 25 percent threshold lose the delegates they otherwise would have won, and those delegates become uncommitted instead.

One way Mr. Santorum could also get some more substantial benefit out of Louisiana if it forced Mr. Gingrich from the race. Otherwise, a win there might not provide much momentum to Mr. Santorum. Previous Saturday events, like the caucuses in Kansas, Washington and Maine, received relatively little news media coverage and Louisiana is especially unsuitable to it since its polls do not close until 9 p.m. Eastern time.

Meanwhile, Mr. Santorum is seeing some troubling polling numbers in other states. In Wisconsin, for instance — which votes along with Maryland and the District of Columbia on Apr. 3 — a recent Rasmussen Reports poll put Mr. Santorum 13 points behind Mr. Romney.

That poll is especially disturbing to Mr. Santorum because he had held a solid lead over Mr. Romney in earlier Wisconsin polls and because its demographics seem reasonably favorable to him. Wisconsin’s demographics and political culture are more like Minnesota (where Mr. Santorum won the caucus easily) or Michigan (where he lost narrowly but which was Mr. Romney’s home state) than Illinois or Ohio.

For these reasons, in fact, I am suspicious that the Rasmussen Reports poll in Wisconsin is a modest outlier. But Mr. Santorum is clearly no longer the favorite there, and if he were to lose the state by anything like the 13-point margin that Rasmussen Reports projects, it could potentially put an end to the campaign.

Wisconsin uses a relatively aggressive delegate allocation method, as do Maryland and the District of Columbia, making it possible that Mr. Romney could win almost all of the 96 delegates at stake on Apr. 3 if he had a good night. That could put Mr. Romney ahead by close to 400 delegates overall even if he lost Louisiana, a commanding advantage that would be close to mathematically impossible for Mr. Santorum to overcome.

Finally, Mr. Santorum is losing ground to Mr. Romney in the Gallup national tracking poll, which now shows Mr. Romney with 40 percent of the vote for the first time. A tracking poll can fluctuate quite a bit, but it is at least possible that some Republicans who like Mr. Santorum but want to avoid a brokered convention are migrating to Mr. Romney.