By Sean Trende - March 9, 2012

The Republican primary has revealed distinct geographic tendencies. Mitt Romney is dominant in New England and in the West. Newt Gingrich has run well in the Deep South, while Rick Santorum has done well in caucus states, the Great Plains, and the peripheral South (it remains to be seen whether his support has bled into Gingrich's strength in the Deep South). That leaves the Midwest as a battleground between Romney and Santorum.

While Romney had a good night on Super Tuesday, the truth is that he did nothing to alter the basic regional nature of his support. He won handily in New England and the West, essentially tied in the Midwest, and ran poorly in the South.

Given the structure of the primary season, this portends a long slog to the nomination, and makes it difficult for Romney to wrap up the nomination early on. Consider the schedule, and the following possible outcomes:

March

The rest of this month is absolutely brutal for Romney.

Great Plains: Kansas. Assume Santorum wins here by a margin roughly equal to that in North Dakota, and wins all the state’s districts except for the 3rd (Kansas City).

South: Alabama, Mississippi, Louisiana. This could go either way between Gingrich and Santorum. Let’s assume that these states have roughly the results of Tennessee, while acknowledging that they could look like Georgia. Romney will probably still win the Birmingham districts in Alabama and the New Orleans districts in Louisiana, but other than that will likely be shut out.

Midwest: Illinois, Missouri. I think the former is fertile ground for Romney, but let’s assume that it is close, like Michigan and Ohio. We’ll have him split the districts 10/8. It’s hard to see Romney running any better in Missouri’s caucuses than he did in the primary, so let’s give the caucuses to Santorum with the same margins as North Dakota.

West: Hawaii. Give this to Romney, at the same rate as Alaska.

Miscellaneous: Northern Marianas, Virgin Islands, Guam, American Samoa, Puerto Rico. Anyone’s guess. Let’s divide evenly among the candidates. Puerto Rico is winner-take-all, so give that to Romney (who has run well with Latinos so far this cycle).

Note that Romney wins only two contests in actual states under this scenario. That is a serious momentum-sapper. Gingrich may have dropped out by this point, or become a non-factor, but since his votes probably go to Santorum, it's probably not relevant to our Romney-centric analysis here.

Rough delegate totals: Romney, 522; Santorum, 314; Gingrich 128; Paul 91.

April

Northeast: Maryland, D.C., New York, Connecticut, Rhode Island, Delaware. Obviously, this is a nice stretch for Romney. There are some question marks here: Who is voting in the Republican primary in Jose Serrano’s 95 percent Obama district in New York? Anyway, we will model New York, D.C., and Maryland after Vermont; Connecticut, Rhode Island and Delaware more like Massachusetts (understanding that we’re probably being too generous to Romney with the latter and not generous enough with the former).

Midwest: Wisconsin, Pennsylvania. Again, assume Wisconsin is similar to Ohio, basically a tie. I think Santorum probably wins Pennsylvania.

Rough delegate totals : Romney, 704; Santorum, 389; Gingrich, 132; Paul 101