KIM LAWTON, guest anchor: Now, religion and the campaigns. Mike Huckabee, a former Southern Baptist minister, bowed out of the Republican race, quoting Scripture and vowing to continue working for the values that dominated his campaign. President Bush endorsed John McCain, but another endorsement generated controversy: Some Catholics were upset by Texas megachurch pastor John Hagee's support for McCain because of past statements Hagee has made about the Catholic faith. On the Democratic side, Barack Obama met with Hispanic evangelical leaders in Texas. But he offended some religious conservatives at a meeting in Ohio when he suggested that the Sermon on the Mount would support gay civil unions. Obama and Hillary Clinton continue to vie for the support of key religious constituencies.

Joining me with more is University of Akron professor John Green, senior fellow at the Pew Forum on Religion and Public Life. John, let's start with the Republicans. With Mike Huckabee now out of the race, what are the religious challenges for John McCain?

Professor JOHN GREEN (Senior Fellow, Pew Forum on Religion and Public Life and Director, Ray C. Bliss Institute of Applied Politics, University of Akron, Ohio): Well, Senator McCain faces a real challenge in unifying the white Protestant evangelical vote behind his candidacy. Even though John McCain has been doing better and better among white evangelicals, on the last primaries in Ohio and Texas Mike Huckabee still won the larger portion of that crucial religious community. And so John McCain needs to make some real effort here in the next few weeks and months to unify that key Republican voting bloc behind his campaign for the fall election.

LAWTON: Can he win without those voters?

Prof. GREEN: You know, John McCain really can't win in a close election without the strong support of white evangelicals, and Democrats are going to make an effort to pull away some of those votes. Senator McCain has had a long history of feuding with the leaders of the Christian right, who have some influence among white evangelicals, and so Senator McCain needs to make a real effort to increase his comfort level with this key Republican constituency.

LAWTON: And in terms of the Democrats, there seems to be a lot of flux among the religious support for Barack Obama and Hillary Clinton. What's going on there?

Prof. GREEN: Now there does seem to be a lot of change. If you look at the last month, from the original Super Tuesday on February 5 all the way up to the most recent Super Tuesday on March 4, we've almost come full circle back to the original coalitions. Senator Clinton originally drew very well among white Catholics, white Protestants. And Senator Obama did very well among black Protestants and the unaffiliated and younger members of white Christian churches. But by Ohio and Texas, we've come back to where we were before. Obama had made some real gains in between those two dates, appealing to white Catholics and white Protestants. But apparently we're back to ground zero, so the campaign will continue.

LAWTON: Why do you think that happened? Why did Obama, who did seem to be expanding his religious coalition, why did he seem to lose ground among some of those groups?

Prof. GREEN: You know, it's really quite interesting. It may very well be that Senator Obama is not very well known in some of those constituencies. It could also be that Senator Clinton has some special appeal from all of her years in politics. A lot of Roman Catholics, for instance, remember her book "It Takes a Village" (to raise a child), which speaks to social issues and social welfare concerns in a way that many Catholics understand. And, of course, Senator Clinton herself is a United Methodist in good standing, and so she may have some appeal among white mainline Protestants that Senator Obama was able to make some gains upon, but maybe not fully solidify.

LAWTON: So what does all this mean for some of the races that are still coming up?

Prof. GREEN: Yes, it could be very important as we go forward. One of the important states that comes up next is Pennsylvania, a state very much like Ohio with lots of white Catholics and white Protestants. But then there are some other states that may help Senator Obama, such as North Carolina and Mississippi, where there's a large number of black Protestants but also a number of young white evangelicals that seem to be very enthusiastic about his campaign.

LAWTON: And which groups will you be watching most closely?

Prof. GREEN: As we go into the fall election I'm going to watch white Catholics, even for the remaining of the primaries, and also young white evangelicals.

LAWTON: All right, John Green. Thank you very much.

Prof. GREEN: You're very welcome.

LAWTON: For more of this conversation, go to my blog on the One Nation page.