As Republican leaders push the party to coalesce around Mitt Romney's candidacy, a question lingers: Is Romney's disconnect with sizable numbers of GOP voters based on ideology or instead on religious belief?

The answer: Both.

Romney's weakness among evangelicals is the more critical stumbling block. Combining results from all primaries and caucuses to date for which we have exit polls, he's lost very conservative evangelicals by 18 points to Rick Santorum, while winning all other slices of the pie - somewhat conservative and moderate evangelicals, and all non-evangelicals regardless of their ideology. (See full results here, and for a look at Ron Brownstein's take on the data, check here.)

Romney's won just 23 percent support from very conservative evangelicals, landing him third in this group, behind Santorum (41 percent) and Newt Gingrich (29 percent) alike. By contrast, Romney has won somewhat conservative evangelicals by 7 points, very conservative non-evangelicals by 18 and somewhat conservative non-evangelicals by a broad 36 points.

The fact that Romney's done 20 points better among very conservative non-evangelicals (43 percent support across all contests) than among their evangelical counterparts underscores the role of religious belief in these contests. But this isn't the sole factor: Ideology matters, too. Witness Romney's 13-point better showing among somewhat vs. very conservative evangelicals, and his 11-point gap comparing somewhat vs. very conservative non-evangelicals.

Romney's problem with strong conservatives operates in conjunction with his shortfall among evangelicals - naturally, since 45 percent of evangelicals also are very conservative. But these results show that Romney's ideological gap also operates independently of religious belief.

Our last national ABC/Post poll reinforces the point. In a form of statistical analysis called a regression, we find that being very conservative and being an evangelical both predict support for Santorum over Romney - independently, and, in those data, at about equal strength.

These results suggest that Romney's challenges can't be written off solely to doubts among evangelicals. He also faces ideological unease among strong conservatives, religion aside.

This doesn't mean evangelicals and very conservative voters are likely to back Barack Obama in sizable numbers in a general election contest, or even that they may just stay home. The level of antipathy toward Obama in these groups may well be enough to overcome their compunctions about Romney. But it's a dynamic worth watching.

In any case, Romney's weaknesses in these groups are more than outweighed by his clear advantage over Santorum elsewhere - among non-evangelicals, somewhat conservatives and moderates. That broader appeal helps explain why Romney - even with his shortfalls - is well ahead in delegates, and better positioned than Santorum for a general election campaign.