Brown's win means that Democrats don't possess a filibuster-proof Senate majority. The new formula for victory resembles the old one: Gain the votes of New England Republican moderates, as well as old-timers who occasionally buck their leadership.
That's just what happened Monday, when Brown, along with Maine Republicans Susan Collins and Olympia Snowe, voted to defeat a filibuster led by far more conservative GOP leaders.
Also siding with Democrats in the 62-30 tally were Rust Belt Sen. George Voinovich, R-Ohio, and Christopher Bond, R-Mo., an old bull member of the Senate Appropriations Committee. Both are big fans of infrastructure spending that also is provided in the bill - and both also are retiring from the Senate this year, giving them some wiggle room to challenge their party's leaders and conservative base.
Monday's vote cleared the decks for an up-or-down final tally Wednesday.
Does the breaking of a filibuster mean bipartisanship is now alive and well, or a passing fancy?
"Well, it's real, but it's quite modest," said CBS News political analyst John Dickerson. "The Senators didn't come together because they found a new fellow feeling and warm sense of togetherness, but they share a common self-interest, which is dealing with the fact that voters want to see something happen on jobs, see some results.
The bill, by Majority Leader Harry Reid, D-Nev., is undeniably modest, especially in comparison with the $862 billion economic stimulus bill enacted a year ago. It's also significantly smaller than a rival bipartisan bill unveiled earlier this month by two senior senators.
But the measure still features the key job-producing element of that bipartisan accord: A $13 billion measure exempting businesses hiring the unemployed from the 6.2% Social Security payroll tax through December and giving them another $1,000 credit if new workers stay on the job a full year.
It also includes a renewal of highway programs through Dec. 31. Both ideas have wide support in both parties. Mark Zandi, an economist with Moody's Economy.com, estimates the tax credit could spur about 250,000 new jobs.
That's still less than 4 percent of the 8.4 million jobs lost during the recession.
"In the end, it was modest - $15 billion is five times smaller than the $85 billion original bill which broke down because of partisanship," said Dickerson. "So they couldn't agree on the whole meal. They went for the appetizer."
In addition to the hiring tax incentives and highway funding, the bill would extend a tax break for small businesses buying new equipment and modestly expand an initiative that helps state and local governments finance infrastructure projects.
Republicans and some Democrats were unhappy that Reid abruptly dumped about $70 billion in other tax breaks for businesses and individuals, help for the unemployed and additional Medicare payments to doctors from a compromise measure unveiled earlier this month by Sens. Max Baucus, D-Mont., and Charles Grassley, R-Iowa, the chairman and ranking Republican, respectively, on the Finance Committee.
Reid then refused to allow Republicans to try to add them back, inviting a filibuster.
For Brown, joining a GOP filibuster over a parliamentary procedural squabble clearly wasn't the best vote for a new senator from an overwhelmingly Democratic state who had campaigned on a promise to rise above partisan politics.
"I came to Washington to be an independent voice, to put politics aside and to do everything in my power to help create jobs for Massachusetts families," said Brown, whose election last month gave Republicans the 41st vote that could sustain filibusters. "This Senate jobs bill is not perfect ... but I voted for it because it contains measures that will help put people back to work."
Dickerson said Brown, who also appeared at this past weekend's Conservative Political Action Conference, can now point to his vote as a sign of his independence and say to his constituents, "'Look, I said I would do what I promised I would do,' which is always something politicians like to be able to say.'"
Dickerson was not optimistic about similarly bipartisan backing for Mr. Obama's refitted health care plan. "When the president announced this plan on Monday, the denunciations came from Republicans immediately and across the board. They'll have this pow wow at the White House on Thursday, and everybody will be on their best behavior in front of the cameras. But this really doesn't seem to be any room at least as far as the pre-show posturing goes."
The larger Finance Committee bill had included about $33 billion in popular tax breaks, including an income tax deduction for sales and property taxes and a business tax credit for research and development that would be extended through 2010. Those ideas have sweeping support among lawmakers, have been routinely renewed and probably will come up for votes again soon.
Business groups say companies are unlikely to hire workers just to receive a tax break. That means most of the tax benefits would go to companies that would have hired new workers anyway.
"Obviously it's not very efficient," Zandi said. "It's something worthwhile doing as an insurance policy but it's not something one would want to do in any other circumstance."
The White House said Monday that the administration strongly supports Reid's bill but that it wants additional measures to create jobs. Among Mr. Obama's jobs proposals are a $250 payment to Social Security recipients, $25 billion in help for cash-strapped states and redirecting $30 billion in Wall Street bailout money to help community banks lend to small businesses.
"It's a good first step," Mr. Obama senior adviser David Axelrod said. "There's no doubt we need to do more."
Other ideas on the Democrats' legislative agenda to boost jobs include money for retrofitting homes to make them more energy efficient, help for state governments to retain teaching jobs and help for small businesses.
The bill would be paid for in part by a crackdown on international tax cheats, an issue the Internal Revenue Service and the Obama administration have embraced. Also, the bill would delay, until 2020, a tax break for multinational companies that pay foreign taxes. The tax break was passed in 2004 but has never taken effect because lawmakers keep delaying it to raise revenue.