The surge that upended Mitt Romney’s efforts in South Carolina now washes into Florida, a large and diverse state that represents perhaps the stiffest test so far for the Republican Party’s anti-Romney faction.

Florida favors well-funded candidates. Its Jan. 31 primary is open only to Republican voters. The electorate is diverse in religion—Florida has an influential crop of Republican Jewish voters—age, race and ideology. Some issues that clearly cut one way in other states, such as immigration, are thornier in Florida.