I just came across the transcript of an interview with Montana Governor Brian Schweitzer (D) about the REAL ID Act. His characteristic forthrightness makes it refreshing to read.
Here's a key point about the REAL ID Act's attempt to coerce states into complying:
So I spoke with Chertoff and it became apparent to me that Homeland Security needed all the states worse than we needed them to do this thing.
In the early going, many state politicians were cowed by the threat that the federal government would interfere with their constituents' travel plans if they did not go along with national standardization of their states' ID documents.
As this interview makes clear, Secretary Chertoff and the DHS recognized that the federal government would be blamed if the Transportation Security Administration interfered with the air travel plans of millions of Americans.
DHS blinked. And it's not the first time that happened.