The former Massachusetts governors appears to be ahead in Illinois, which votes Tuesday and holds the biggest trove of delegates of any leftover contest this month.

But a recent poll gives Santorum the edge in Louisiana, which votes next weekend. And Missouri, where presidential caucuses are ongoing, would appear to favor the former Pennsylvania senator as well – if the results of the nonbinding primary which Santorum swept are any gauge.

The only other contest this month is Puerto Rico, which holds its caucuses on Sunday. Both Romney and Santorum made in-person appeals on the U.S. island territory this week. While little polling is available, Romney does have the advantage of an endorsement from Gov. Luis Fortuno, who campaigned with the GOP front-runner on Friday.