Rasmussen’s Michigan primary poll shows Santorum leading Romney 35-32%. Given the composition of the 2008 Michigan primary electorate, Romney should be doing better than he is. Santorum has a narrow lead because he has been able to dominate the relatively small “very conservative” portion of the electorate (leading Romney 49-20%) while also winning substantial support from “somewhat conservative” and “other” (i.e., moderate) voters. 42% of “somewhat conservative” respondents support Romney to Santorum’s 30%, and 38% of “other” favor Romney compared to Paul’s 27% and Santorum’s 17%. Romney will have to find some way to consolidate his natural supporters of “somewhat” conservative and moderate voters, or he will need to drive a lot of “very conservative” voters away from Santorum. Failing that, there is good reason to expect Santorum to win Michigan. Even though Gingrich remains in the field, he isn’t splitting the “very conservative” vote very much, which has allowed Santorum to rack up his large lead with these voters.