Summarized nicely by a 538.com commenter:
What turns this from McCain merely answering Reid and Paulson's call to come help bring House GOP members on board to a naked political ploy:
1) Making a big announcement about "suspending his campaign" on national television and making an irrelevant call to postpone the debates.
2) Not actually leaving NY or canceling any appearances until it was already time to bring a proposal to Paulson and the President.
3) Not contacting the banking committees in both the Senate and the House to learn of the negotiations on the proposal.
4) Not following-up any potential meeting with the Congressmen actually working on the proposal with a meeting with the House delegation opposing it *before* any compromise could be presented to the White House.
5) Sitting silently through the White House meeting instead of, oh, I don't know, *actually trying to negotiate a compromise*.
You are right that Reid et al. asked McCain to step up and show some leadership on this. He didn't. He stepped and grandstanded on it, and did absolutely nothing to help negotiate a working compromise. Instead his actions seemed to have given the dissident GOP House delegation cover not to reach any compromise at all. And his only motivation for doing this would be to take over another news cycle.
What McCain *could* have done would have been to quietly cancel his interview appearances and his talk to Clinton's Global Initiative to return to Washington to help broker the compromise. He could have quietly worked to bridge the gaps between at least most of the House GOP and the compromise worked out *within* the banking committee. If he had done this, no doubt he would have gotten a lot of well-deserved praise that would have played *very* well in the media, and would have fostered his image as a bipartisan bridge-builder.
But, the fact is, he's gone and done the opposite, and his actions appear to have set the bailout bill back tremendously. This is about the worst example of leadership in a crisis I can imagine.