MESA, Ariz. (AP) — A bitter and often personal debate behind them, Republicans Rick Santorum and Mitt Romney are shoring up their campaigns in different ways ahead of a series of crucial presidential primaries.

Romney is paying the most attention to Michigan, his birthplace and the site of an unexpectedly tight race with Santorum, by attending a tea party rally Thursday night in an effort to get more conservative support. He has campaigned confidently in Arizona, so much so that he has not aired any television ads in the state.