Making the right accusations...

There are enough people shouting Crisis that McCain doesn't have to persuade anyone the problem is severe. The collapse of the deal came from the Democrats' (appropriate) requirement that Republicans share the responsibility by voting for the legislation, and many House Republicans' refusal to do so. McCain is safe on that score as well.

With the President's ability to chair any meeting with any list of attendees, McCain can be involved. And he does have practice getting legislation passed in the Senate, which can be highlighted with the cooperation of fellow Republicans.

Note that those statements are not meant to imply McCain will solve the economic and legislative problems, but that he can appear effectively involved.

What McCain cannot escape is being a Republican. And the Republicans are - so far - being blamed for a problem which has... caught people's attention. Expect ads including the involvement of Democrats (as in voting for blameworthy legislation) when McCain starts to try to salvage the situation.