The four other GOP senators who broke ranks -- Olympia Snowe and Susan Collins of Maine, George Voinovich of Ohio and Christopher "Kit" Bond of Missouri -- also were criticized on Tuesday. But Brown was the big target on conservative Web sites, talk shows and even the Facebook page his campaign has promoted as an example of his new-media savvy.

"We campaigned for you. We donated to your campaign. And you turned on us like every other RINO," said one writer, using the initials for "Republican-In-Name-Only."

The conservative-tilting Drudge Report colored a photo of Brown on its home page in scarlet.

The new senator responded by calling into a Boston radio station.

"I've taken three votes," Brown said with exasperation. "And to say I've sold out any particular party or interest group, I think, is certainly unfair."

The senator said that by the time he seeks re-election in two years, he will have taken thousands of votes.

"So, I think it's a little premature to say that," he said.

Senate Republican leader Mitch McConnell of Kentucky wasn't particularly perturbed about Brown's vote, saying his election last month has "made a huge, positive difference for us and for the whole legislative agenda."

"We don't expect our members to be in lockstep on every single issue," McConnell added.

Political observers said each of the five Republican senators had solid reasons locally for voting as they did, to cut off a potential Republican filibuster on the bill.

The measure featured four provisions that enjoyed sweeping bipartisan support, including a measure exempting businesses hiring the unemployed from Social Security payroll taxes through December, and giving them a $1,000 credit if new workers stay on the job a full year. It would also renew highway programs through December and deposit $20 billion in the highway trust fund.

It faces a final Senate vote Wednesday.

Snowe and Collins hail from economically ailing Maine, and they can't stray too far from the Democrats who populate much of New England. And Voinovich and Bond also are from states hard hit by the recession.

The latter two also have the ultimate protection from retribution: They're not seeking re-election this fall.

"When you have decided to retire and you are a free agent, you can pretty much do what you want," said Peverill Squire, a political scientist at the University of Missouri-Columbia. And Squire doubted that Bond, retiring after 24 years in the Senate, would have paid much of a political price even if the famous appropriator were seeking re-election. Continued...