Mickey Kaus sees signs that the Democrats will try to prevent the border fence from being built. This would be an obvious example of overreaching – while the politics of immigration are vexing and the public may be willing to accept a compromise solution including legalization of existing illegals and a guest worker program, public opinion will turn very quickly against the view that there should be no additional enforcement on the border.
(Of course, knowing the Dems they will counter the perception of lax enforcement by adding a bunch of additional funding for new Border Patrol agents but no meaningful authority for them to accomplish anything, thus treating enforcement of the law as just another jobs program for unionized government workers)