Didn't most of the Republicans in the House vote for border security only? They are all up for reelection this year. Only a few Republican Senators are, but I seem to read that Republicans are for amnesty. Doesn't the House count at all?
The house depends on Hastert's honor. He has promised not to put forward any bill that is not "majority-majority." That is, he will not put forward a bill favored by a minority of R's and a majority of D's. So a shamnesty could pass, if Hastert is rolled on his "majority-majority" policy. And if a shamnesty passes, it will be a bloodbath for Republicans in November.