"Comprehensive climate change legislation" = McCain political speak for carbon cap-and-tax
McCain is signaling that he will support cap-and-tax as long as nuclear power is tacked on.
He is also trying to wrest control of the issue away from other conservatives and deliver political cover to Obama.
If you think he's right on that, then you've got some issues to work out.
As we have seen time and again it is easy for Congress to tack on a "gimme issue" into a bill and then forget all about it. It can call for 'research' into nuclear power plants and then just let it get bogged down to its death in bureaucracy. McCain's main aim has been to be the one who can take credit for 'fixing' Global Warming. His record is clear.