Mitt Romney holds a wide lead over other GOP contenders in a new Washington Post-ABC News national poll, but his support continues to lag among core Republican constituencies and he faces an uphill battle appealing to those not already backing his candidacy.

Overall, 39 percent of Republicans and GOP-leaning independents support Romney (or already backed him in a primary or caucus), his best showing in Post-ABC polls since last summer. Newt Gingrich clocks in at 23 percent, with Rick Santorum and Texas Rep. Ron Paul garnering 16 and 15 percent apiece.

But Romney still struggles against his rivals among strong conservatives and religiously focused voters. Still, these groups have failed to coalesce behind a Romney alternative, splitting their support between Gingrich and Santorum.

After a raft of debates and five primaries and caucuses, many Republicans are souring on their alternatives. A majority — 56 percent — of those who are Gingrich, Santorum and Ron Paul supporters say the more they hear about Romney, the less they like him. Nor is this merely a problem in the nominating contest: By better than 2 to 1, political independents say the more they learn about Romney the less they like rather than more they like him.

Romney’s weak groups splintered

Romney earns just 25 percent support among “very conservative” Republicans and GOP-leaning independents and 27 percent among white evangelical Protestants. Among those who say a candidate’s religious beliefs matter at least somewhat, Romney scores 24 percent, compared with about double that — 50 percent — among those less concerned with a candidates’ religiosity. These all were among his weakest groups in Iowa, South Carolina and Florida contests in January.

Both Gingrich and Santorum outperform among Romney’s weakest groups, but neither clears the 33-percent-mark among strong conservatives, evangelicals or religiously focused voters. Despite vying for some of the same supporters, Republicans do not see Gingrich and Santorum as equals. Gingrich clearly tops Santorum on dealing with the economy and budget deficit, having the best experience to be president and being able to defeat Obama in a general election.

Santorum runs closely with Gingrich on social issues and empathy, but far outpaces the former speaker on honesty. Nearly a quarter of Republicans say Santorum is the most honest and trustworthy (24 percent), compared with 7 percent who say this of Gingrich.

Despite Romney’s lackluster support among these Republican base groups, unifying the “non-Romney” vote may not be as simple as Gingrich or Santorum dropping out and endorsing the other. Nearly three quarters of those supporting a candidate other than Romney say their decision is an affirmative one, not merely “against” Romney.

The religion factor

Three out of four Republicans say Romney’s Mormon faith is not a major factor in their vote choice, but religiously focused Republicans tend to shy away from the front-runner. Over four in 10 Republicans say a candidate’s religious beliefs matter to them, and Romney wins only 24 percent support among this group, compared with 50 percent among those who say religion matters less. Both Gingrich and Santorum perform twice as well among those who say a candidate’s beliefs are important than other Republicans

Romney continues to struggle among white evangelical Protestants, who have made up between 21 and 64 percent of voters in early primaries and caucuses. In this poll, Gingrich and Santorum win 30 and 28 percent of white evangelicals, respectively, while Romney garners 26 percent of their support. Nearly seven in 10 white evangelicals say a candidate’s religious beliefs matter to them, and more than a quarter say Romney’s Mormon faith is a major reason to oppose him.

Heard enough?

Views on Gingrich are less split: 47 percent of Republican leaners are growing less fond of the former Speaker as they hear more, 31 percent like him more. More than a third of “very conservative” Republicans — his group of strongest supporters — say they like Gingrich less the more they hear.

Romney’s wealth

By a more than a 2 to 1, Republicans and GOP-leaning independents see Romney’s wealth as a positive factor because it represents his achieving the American dream rather than benefiting from opportunities that are not available to most people. Republicans with incomes over $100,000 are 21 percentage points more apt to see Romney’s wealth as a positive factor than those earning less (78 to 57 percent).

There’s a bigger divide over whether Romney has paid his fair share in taxes. More than half of Republicans without college degrees say Romney’s 14 percent effective tax rate was insufficient, while nearly two in three college-educated Republicans took the opposite view.

Views of Romney’s tax rate are worse among some of his strongest groups of supporters. A 56 percent majority of moderate and liberal Republicans see Romney as not paying his fair share, a group who backs Romney by 30 points over his challengers.

Read the full poll results and methodology

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