Bob Fertik, president of Democrats.com, a progressive Web site, started asking his readers last month to pledge money to an escrow fund for Mr. Obama, as opposed to contributing to him outright. The idea was to make Mr. Obama rethink his decision to support the Bush administration’s wiretapping measure.

Mr. Obama initially said he would try to filibuster a vote, but on Wednesday he was among 69 senators who voted for the measure, which to many liberals represents a flagrant abuse of privacy rights. The legislation grants legal immunity to telecommunications companies that cooperated with the wiretapping program.

So far, 675 people have pledged $101,375 to Mr. Fertik’s escrow fund, money that theoretically would be donated to Mr. Obama once he showed a firm commitment to progressive values, Mr. Fertik said.

But Mr. Fertik also said that while Mr. Obama’s change on the spying issue upset some supporters, it was not necessarily emblematic of a troubling shift to the center. He said he continued to support the senator, though he added, “We don’t see the need to close our eyes and hold our noses until November.”

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