BOSTON (AP) — During the 2010 special election to fill the seat left vacant by the death of U.S. Sen. Edward Kennedy, then-candidate Scott Brown vowed to be the “41st” vote against President Barack Obama’s sweeping health care overhaul.

Two years later, the Republican Massachusetts senator still opposes what he calls “Obamacare” but has found a lot more to love about the Democratic president and his agenda.

While many Republican lawmakers have used Obama as the ultimate campaign foil, Brown has touted his bipartisanship as a key asset in his re-election bid as he hopes to fend off a challenge from his chief Democratic rival Elizabeth Warren.

As proof, Brown has gone out of his way to highlight common ground with Obama.

When Obama called on Congress during his State of the Union speech to “send me a bill that bans insider trading by members of Congress, and I will sign it tomorrow,” Brown, who sponsored the bill, was quick to highlight the endorsement.

As Obama was exiting the House chamber after the speech, Brown buttonholed him on the issue.

“My insider trading bill is on Harry’s (Majority Leader Harry Reid’s) desk right now,” Brown told Obama, shaking his hand. “Tell him to get it out.”

“I’m going to tell him,” Obama replied. “I’m going to tell him to get it done.”

The brief exchange played out before television cameras, and a press release issued by Brown’s Senate office included a link to the clip of the video posted on YouTube by Brown’s campaign. The Senate passed the bill Thursday on a 96-3 vote.

Brown has also been a key swing vote in the Senate. He supported a Democrat-backed overhaul of the nation’s financial system, and his vote to repeal the military’s “don’t ask, don’t tell” ban on gays serving openly also drew criticism.

Brown broke even further from his fellow Senate Republicans in backing Obama’s decision to bypass the Senate in January and appoint Richard Cordray to lead the new Consumer Financial Protection Bureau.

The Senate’s top Republican, Mitch McConnell of Kentucky, accused Obama of an unprecedented power grab that “arrogantly circumvented the American people.”

But Brown, who had welcomed tea party support during his special election campaign, issued a statement lauding the appointment.

“If we’re going to make progress as a nation, both parties in Washington need to work together to end the procedural gridlock and hyper-partisanship,” he said.

Part of Brown’s embrace of Obama has to do with the Massachusetts electorate, which is more used to electing Democrats to office than Republicans.

Not only is Brown is the only GOP member of the state’s congressional delegation, but Democrats hold every other statewide seat in Massachusetts; Gov. Deval Patrick is a close ally of Obama.

Another likely reason why Brown is highlighting his policy ties to Obama is the presence of Warren in the race.

The Harvard professor and consumer advocate has captured the imagination of Democrats in Massachusetts and nationwide. She’s also proved adept at pulling in millions in campaign donations.

Warren raised $5.7 million during the final three months of 2011, eclipsing Brown’s $3.2 million for the same period. Brown still enjoys an overall money advantage with $12.8 million in cash on hand, compared to the more than $6 million Warren has in her account.

Recent polls show the two locked in a close race.

The more Brown can show his bipartisan streak, the more he may be able to blunt a Warren surge — particularly in an election year when Obama’s name will be on the ballot, another big draw for voters in a state where the Democratic president remains popular.

Warren’s campaign has worked to tie Brown to the GOP, saying he’s backed tax breaks for oil companies and has spoken out against a proposal by Obama to require people making more than $1 million a year to pay at least 30 percent in taxes.

“Scott Brown’s endorsed Mitt Romney, not President Obama, and on important issues — the Buffett rule, jobs bills, and tax breaks for oil companies — Scott Brown has turned his back on Massachusetts and on President Obama to stand with and vote for the interests of Wall Street, big banks and big oil,” said Warren press secretary Alethea Harney.

Brown has said he’s just showing what he says is his independent streak by looking each issue individually and deciding what he thinks is best for Massachusetts and the country, regardless of party affiliation.

That emphasis on Brown’s “independent voice” could be critical in November.

While Massachusetts tends to elect Democrats, the majority of voters in the state are not registered with either party.

It was by appealing to those independent voters, and picking off moderate Democrats, that Brown was able to win in 2010. While that campaign was compressed into a few weeks — allowing Brown to ride a wave of popularity — the current campaign will play out between now and November.

There are limits to Brown’s bipartisanship.

During a campaign kick-off rally in Worcester, Mass., Brown — speaking to a more partisan crowd — only invoked Obama’s name when he called for the repeal of what he called “Obamacare.”

“One unfinished fight is the effort to get rid of Obamacare. A government takeover of health care was a bad enough idea to start with, and the way it was rammed through was even worse,” he told the cheering crowd. “I was against Obamacare then, and I am for its repeal today.”

Massachusetts Democrats have struggled to find a way of targeting Brown as he highlights areas of agreement with the president.

As Brown spotlighted Obama’s support of his anti-insider trading bill, Democrats said Brown should go a step further and back another Obama proposal to limit any elected officials from owning stocks in industries affected by their votes.

“Scott Brown should join President Obama and Senate Democrats’ call to ban members of Congress from owning stock in companies they influence if he is really serious about cleaning up Washington,” said Massachusetts Democratic Party spokesman Kevin Franck.

The Senate campaign could end up being the most expensive in Massachusetts history.

Last month, Brown and Warren took the unusual step of signing a pledge to curb political attack ads by outside groups in their Massachusetts Senate race. Under the terms of the deal, each campaign would agree to donate half the cost of any third-party ad to charity if that ad either supports their candidacy or attacks their opponent by name.