Because both sides of the isle have already signed on to the North American Union idea and don't want to put up any roadblocks to that. So the focus will be on the WOT and home foreclosures.
The democratic stance on illegal immigration won't demoralilze and keep traditional midterm democratic voters at home.
The GOP stance on illegal immigration will demoralize and keep traditional midterm GOP voters at home.
The democrats don't have to be right or better on this issue as the democratic voters don't generally care that much, they just need the Republicans to be wrong.