Coakley-Brown Senate Race High-Stakes for Dems, Health Care Overhaul

President Obama is planning a last-minute visit to Massachusetts to campaign for an embattled Democratic candidate there as concern mounts among national and state party leaders about the possibility of ceding their 60th Senate vote to Republicans.

The entry of Obama into the campaign comes as the battle between Democratic state Attorney General Martha Coakley and Republican State Sen. Scott Brown appears surprisingly close in some polls before Tuesday's election with Democrats increasingly on edge.

White House spokesman Robert Gibbs took a shot at Brown during a press briefing today, saying Brown "feels comfortable fighting for the insurance industry and big banks." Gibbs also described the special election as "a referendum on who's side are you on," not on President Obama.

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Massachusetts, where registered Democrats outnumber Republicans by more than three to one, has long been a Democratic stronghold, sending two Democratic senators to Washington for each of the past 31 years.

Obama's visit, as well as other high-profile Democrats', signals a last ditch effort to try to energize the Democratic base and counteract what some party members speculate has been a defection of independent voters to Brown.

Former President Bill Clinton is appearing with Coakley at two campaign events today. Ted Kennedy's widow, Vicki, is appearing in a television ad, and earlier this week President Obama taped a last-minute phone appeal.

VIDEO: Nude photos surface of Scott Brown, the Massachusetts candidate for U.S. Senate.Play

In a robo-call going out across Massachusetts today, Obama says he rarely makes such calls but "the stakes are so high."

Click HERE to listen to the robo-call.

At risk for Democrats is a key senate seat, the legacy of a political dynasty and maybe even the future of national health care legislation. Democrats have a bare legislative majority in the U.S. Senate with 60 votes, and losing the Massachusetts seat to a Republican could prove decisive.

If elected, Brown said, he would vote against the Democrats' health care overhaul bill "It's not good for Massachusetts and it's, quite frankly, not good for the country," he said.

Fearing such a possibility, national Democratic groups have poured more than $1 million into the campaign to retain their stronghold in one of the bluest of blue states.

A late fundraising appeal by Vicki Kennedy generated $500,000 in six hours earlier this week, a Democratic National Committee official said, which is one sign of how nervous many Democrats are.

Kennedy's senate seat has been occupied by Sen. Paul Kirk, a Democrat, since his gubernatorial appointment in September, a month after Kennedy's death.

But Republicans, including candidate Brown, are optimistic that Democratic domination of Massachusetts' Senate seats may soon be history.

"With all due respect, it's not Ted Kennedy's seat, it's the people's seat," Brown, 50, said during a recent debate with his rival.

The state senator's candidacy has energized Republicans and Tea Party activists who have poured money into the state to help him campaign. A Republican source familiar with Scott Brown's fundraising told ABC News that Brown has raised more than $1 million online every day this week.

"There's real energy," Brown said. "My phone banks are full. We raised $1.35 million in a day. And I'm going to use every penny of it to fight back against the onslaught that's coming."

Coakley, Brown Ads Go Head-to-Head in Final Stretch

Brown, a lawyer and former model, has run a creative and spirited campaign but has also been cautious about identifying as a party-line conservative in a state where registered Democrats outnumber Republicans.

In one ad, Brown associates himself with Democrat and former President John F. Kennedy.

Historical footage of JFK pledging that money be "placed in the hands of consumers and businessmen will have both immediate and permanent benefits" to the economy is followed by Brown, who adds a conservative twist, saying "every dollar released from taxation" will have a similar effect.

"[Republicans] want this, they smell it, there is blood in the water here and they are coming after this seat," Boston Globe statehouse bureau chief Frank Phillip said.

For her part, Democrat Coakley has brushed off speculation about a Republican victory, saying polls suggesting a tight race are inaccurate.

"We don't know that it's close," Coakley said. "We've got polls all over the map here, and one of the reasons is people are not making up their mind or changing their minds."

Coakley, 56, who has dominated the spotlight as Massachusetts' attorney general and prosecutor in the famed Louise Woodward nanny trial in the 1990s, has largely campaigned on the same ideals shared by Kennedy.

Recently, she shifted her campaign focus to painting an image of Brown as a "conservative Republican," an unwanted label in such a staunchly blue state.

"Who is Scott Brown, really? A Republican in lock-step with Washington Republicans," one of her latest ads says. "In times like these, we can't afford a Republican like Scott Brown."

The shift to the negative is yet another sign of how much is at stake for Coakley and the Democrats.

"[Democrats] are in big trouble in November if they lose this," the Boston Globe's Phillips said.

While most Democratic insiders remain confident Coakley will win, that it is even close is "embarrassing," one of them said.

ABC News' Rick Klein, David Chalian and Teddy Davis contributed to this report.