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President Obama warned Massachusetts voters Sunday from following Republican Scott Brown's old pickup truck around the state, saying if elected to the U.S. Senate, Brown will drive health care and the rest of the Democratic agenda off track.

In a quip he repeated several times during a campaign appearance for Democrat Martha Coakley, Obama mocked the man who has been driving a pickup truck around the state, claiming he's a "lockstep" Republican.

"Martha's opponent already is walking in lockstep with Washington Republicans," Obama said, criticizing Brown for opposing the president's proposed tax on Wall Street. "She's got your back, her opponent's got Wall Street's back. Bankers don't need another vote in the United States Senate. They've got plenty. Where's yours?"

Obama also took jabs at Brown's signature vehicle, and his "slick ads."

"So look, forget the ads, everybody can't can slick ads. Forget the truck. Everyone can buy a truck."

Brown took that opportunity to slam the president on government spending..

"Mr. President, unfortunately in this economy, not everybody can buy a truck," Brown said in a statement. "My goal is to change that by cutting spending, lowering taxes and letting people keep more of their own money."

Coakley, whose race against Brown has narrowed to a toss-up as voters zero in on the cost of a massive health insurance bill in Congress, got a boost from the president during a Sunday afternoon rally at Northeastern University in Boston. Democrats are hoping the president's popularity with young people will reinvigorate the case for Coakley, whose lost her edge to Brown in recent polling.

Coakley has been criticized for not engaging enough in retail politics and not buying enough advertising. Brown has since moved from riding around the state in his pickup to a tour bus he rides to pancake breakfasts and diners.

"She let it become a personality contest and that was a mistake," said Rep. Barney Frank, D-Mass., who has warned that a Coakley loss could kill health insurance reforms Democrats are pushing for in Congress. "Some of us complained about it and we think it's turned around."

But Sunday's rally was not the typical Obama function. The hall where they gathered was only partly filled, and supporters standing behind the guests of honor appeared caught off guard as an abortion protester and a young boy accompanying him were removed from the building.

With polling -- and momentum -- seemingly breaking toward Brown, he has become the target of a scathing attack ad that accuses him of wanting to turn rape victims away from hospitals because as a state senator he supported a conscience clause that would have allowed medical workers to refuse to give "day-after" pills to end pregnancies.

Another effort by the Democratic National Committee attempts to link Brown to the "birther" movement which claims Obama is not a natural American citizen by noting that during a 2008 conversation about the pregnancy of Sarah Palin's daughter Bristol, Brown said he didn't know whether Obama's mother was married when he was born.

"Scott Brown has proven that he shares the values of the fringe right-wing that sprouted birthers and death panels," said DNC Communications Director Brad Woodhouse.

Brown has been gaining ground mainly by discussing the tax implications of the 10-year, $1 trillion health insurance plan congressional Democrats are trying to pass.

"Regardless of who wins, we have here in effect a referendum on this national health care bill," Senate minority leader Mitch McConnell, R-Ky., told "Fox News Sunday." "The American people are telling us, 'Please don't pass it'"

If Brown becomes the 41st Republican in the U.S. Senate, that means Congress may have only a few days to pass a bill that he could effectively stop as the key vote in the filibuster process. However, Republicans have expressed concern that the state's Democratic leadership could hold  up the certification process that would seat Brown in the Senate post held by the late Sen. Ted Kennedy for 47 years.

"The first step is to see what the people of Massachusetts say on Tuesday and then look at the process for seating," McConnell said. "Whoever it is should be sworn in promptly."

The last time a Republican won a Senate seat in the state was in 1972. Special elections are generally lower-turnout races and Democrats are doing what they can to stimulate reliable voters in a state that is about 50 percent unaffiliated.

Obama is personally popular in the state, but his job approval rating is 48 percent. Only 36 percent of Massachusetts voters approve of the health care bill wending its way through Congress.

Since taking office a year ago, Obama's track record for helping other Democrats hasn't been stellar. He campaigned hard for New Jersey Gov. Jon Corzine who ran for re-election last year and in Virginia for Creigh Deeds, the Democratic nominee to replace outgoing Democratic Gov. Tim Kaine. Both lost.

The president was also rebuffed after making a high profile pitch for his home city of Chicago to host the 2016 Olympics. After traveling to Copenhagen last fall to personally make the city's case, the International Olympic Committee rejected Chicago's bid on the first ballot.

Nonetheless, the joint appearance by Obama and Coakley is in many ways marriage of a necessity.

Coakley is depending on his star power to boost Democratic turnout, particularly among blue collar and minority voters who might not be motivated to vote. And Obama, whose political muscle has weakened amid the still struggling economy and his push for a controversial health care package, will see much of his legislative agenda threatened if Coakley loses.

"Understand what's at stake here Massachusetts. It's whether we're going forward or going backwards," the president said, the urgency clear in his voice as he tried to energize his dispirited base in this Democratic stronghold. "If you were fired up in the last election, I need you more fired up in this election."