After long opposing the idea of immunity for the phone companies in the wiretapping operation, [Senator Barack Obama of Illinois] voted for the plan on Wednesday. His reversal last month angered many of his most ardent supporters, who organized an unsuccessful drive to get him to reverse his position once again. And it came to symbolize what civil liberties advocates saw as “capitulation” by Democratic leaders to political pressure from the White House in an election year.

Senator Hillary Rodham Clinton of New York, who was Mr. Obama’s rival for the Democratic presidential nomination, voted against the bill.