From a purely political perspective, John McCain should come out against this bailout.
1) The credit crisis has helped Obama regain the momentum in the race because people equate Wall Street with Republicans. And generally, people trust Obama more on the economy than McCain.
2) The Dem collapse on offshore drilling, plus the drop in oil prices, takes a bit of the steam out of McCain's "drill here, drill now" campaign theme.
3) Other than one poll, public surveys show the public deeply distrustful of government bailouts.
4) If McCain wants to change the momentum of the race back to his favor, he has few remaining opportunities. There are the debates. He could come in favor a big middle-class tax cut. And he could come out against the "Obama-Bush" bailout bill.
5) Of course, the risk is that if he comes out against the plan and the plan dies and the market tanks, he could be blamed.