Senator John McCain had intended to ride back into Washington on Thursday as a leader who had put aside presidential politics to help broker a solution to the financial crisis. Instead he found himself in the midst of a remarkable partisan showdown, lacking a clear public message for how to bring it to an end.

At the bipartisan White House meeting that Mr. McCain had called for a day earlier, he sat silently for more than 40 minutes, more observer than leader, and then offered only a vague sense of where he stood, said people in the meeting.