That "anti-illegal crowd" (and they are the overwhelming majority) is yelling that the Repbublicans are untrustworthy BECAUSE THEY ARE!
This double-cross, just the latest of many on this issue by the Republican elites who don't give a damn about the middle class, is probably the straw that broke the camel's back.
Like 1974, they can't take the lies and duplicity anymore, and they are going to stay home. Until now, there was hope, and the election might have been close. Now it will be a disaster. A 50 seat loss in the House and an 8 seat loss in the Senate can be expected. Let's see how traitors like Warner and McCain and Hagel and Graham like life in the permanent minority. (Actually, they have acted as if they were in the minority the last 12 years, so it shouldn't bother them too much.)
Who cares if the Democrats take over and the war is lost if in 30 years America will resemble Mexico? With the Republican elites in concert with the Democrats screwing the hardworking conservative middle class, let's throw in the towel and start living off the welfare state. Except for the occasional riot, Paris is still pretty in the spring.
OK, I guess you can take the loss and try to grab it as a repudiation of their treachery -- but the republicans are going to think it's because they tried to appeal to the anti-illegal people but they didn't show up anyway, and realise they should have tried to woo the pro-illegal crowd, since the democrats won with that position.