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 more 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.

Santorum is focusing for the moment on raising money for his cash-strapped operation. He is hoping for an upset in Michigan, which would cap a rebound that began two weeks ago with victories in three states.

The 20th debate of the primary season offered the GOP hopefuls their final face-to-face outing before contests over the next 12 days that may well winnow the field.

CNN anchor John King asked the candidates to address their views of contraception, a subject that has risen as a point of contention in the GOP field. The audience at Wednesday's debate booed and the candidates tried to dodge discussion of views that could prove problematic come the general election.

Gingrich says he prefers to discuss Obama's support for "infanticide," and Romney says Obama is attacking "religious tolerance." Ron Paul, a physician, says immorality leads to the need for contraception, not the other way around.

Santorum says he opposes contraception and says the nation needs stronger families, not birth control.

On the topic of immigration, Gingrich says he would devote as many resources as necessary to securing the U.S.'s southern border and that he would build two separate fences at the border to make it more difficult to cross illegally. He also says he'd send thousands more employees of the Homeland Security Department to border areas.

Romney says he would put more resources into securing the border and support programs that make it more difficult for illegal immigrants to work in the U.S. He says Arizona's approach to illegal immigration is a "model" for the country.

Santorum says he would also beef up efforts to combat illegal immigration.

Copyright 2012 by The Associated Press. All Rights Reserved.