The Reps in Congress weren't weak on immigration, the WH was. And attributing the Dems' victory in the 2006 to Rep voters and immigration is demonstrably false. All elections are local. You need to look at each race individually and determine what the factors were by district and state. The War in Iraq, Rep scandals like Cunningham, Foley, Abramoff, etc. played into the hands of the Dems. They had a remarkable turnout for the midterms because their base was energized.
But the truth doesn't make for good debating points, so it will be ignored wholesale.
If I can I would like to add that the RNC, Bush, Rove, et al ran a horrible campaign. The democrats gave the RNC a ton of great quotes to use but didn't. The republicans ran at best a lack luster campaign and paid the price. We lost the middle because we didn't give them a reason to show up. I still have the nagging feeling that Bush and Rove weren't all that upset as they are still seeking the holy grail of this administration...Comprehensive Immigration Reform. The loss of the last election is the only way they can get what they seek.
Add GOP support for unrestraint free trade which have closed many factories in rural southern and mid west districts that usually vote GOP. MFN and CAFTA doomed the GOP candidate in those districts.
I like it.
Add a rider that all troops before or after deployment must spend 60 days on the border either training up for foreign deployment of being debriefed on their deployment.
That would drive a stake through Reid and Clintons heart.