It will be seen by the GOP establishment as the fall of one man, not a rebuke to their amnesty agenda
After a series of defeats, a Tea Party candidate finally claimed a major scalp. Cantor had never been a particularly strong candidate and the Tea Party benefited from having a large committed turnout, while Cantor's voters stayed home.
It's tempting to celebrate Cantor's defeat as the end of amnesty. But it's unrealistic.
The GOP establishment has seen plenty of warning signs, but it has moved forward nonetheless. Its response to an amnesty setback is to retool the lies they're telling. They can't give up on the agenda because it's all they have to cling to after the 2012 defeat and it's backed by wealthy and powerful special interests.
The establishment will be staggered, but its consultants will put together an explanation and the story will be spun and respun. Cantor's loss will be treated as an outlier that happened as a result of an unlikely converge of circumstances. The survival of the establishment candidates, even noxious ones, will be seen as proof of that. If Graham can win, then the fault was in Cantor. If Boehner can win, then the fault was in Cantor. It's what they will keep telling themselves.
Privately some GOPers will step a bit more carefully, but they will no more back down from amnesty after one defeat than Obama backed down from his policy agenda after 2010.
Politicians respond to a setback by copying the language of some of their opponents and then looking for a way to relaunch their agenda. It takes multiple humiliating defeats for that to change.
Cantor's loss is painful, but it will be seen by the GOP establishment as the fall of one man, not a rebuke to their amnesty agenda.
A single setback won't stop amnesty. Only a sustained effort will.