The antipathy runs deepest among the most conservative bloc of voters -- blue-collar whites -- and in places where many Republicans draw their support, rural areas. Forty-five percent of whites without a college degree said they are less likely to support lawmakers voting for the measure. Just 15 percent said they would be more likely to back them, while 33 percent said it wouldn't make a difference.

Among rural voters, 45 percent said they'd be less likely to back the incumbent, while 41 percent of them said it wouldn't make a difference. Just 12 percent said supporting the measure would improve the sitting lawmaker's chance of drawing their vote.

The conservative base's continued opposition to a pathway to citizenship -- and their promise to seek retribution on elected officials who think differently -- highlights a central problem facing Republicans as party leaders try to retrofit the GOP's message and agenda on this and other issues: In many cases, it's simply not in a GOP lawmaker's self-interest to adopt a centrist, moderate position. Adjustments that might be necessary for the party to win back the White House in 2016 often conflict with short-term interests of House or Senate members more worried about their own reelection in 2014.

But GOP lawmakers in upscale, suburban states and districts might find greater forgiveness.

College-educated whites are almost perfectly split on the question: 30 percent said it would make them more likely to support their representative in Congress, 33 percent said the opposite, and 32 percent said it wouldn't make a difference. Suburban voters were less tolerant, but still more open than their rural counterparts. Thirty-six percent said backing the measure would make them less likely to support their lawmaker, while 37 percent said it wouldn't affect their vote.

For their part, Democrats are not likely to shower favor upon incumbents who support the bill. Many, 49 percent, said it won't affect their vote; otherwise, by a 29-19 percent margin, they said support for comprehensive immigration reform makes them more likely to back the incumbent rather than less likely.

Independents side with Republicans on the question, although with less fervency. Thirty-five percent of them said they will be less likely to back a lawmaker who supports comprehensive immigration reform, while only 19 percent said it would make them more likely to support the incumbent. Still, a plurality, 44 percent, said the issue won't weigh on their decision during next year's midterms.

The relative lack of interest from Democrats, combined with the GOP-leaning position among independents, creates further disincentive for Republicans, who are unlikely to find much general-election reward for their vote if they survive a primary.

The poll of 1,005 adults, conducted by Princeton Survey Research Associates International from June 20 to June 23, included both landline and cell-phone respondents. It has a margin of error of plus or minus 3.6 percentage points.

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