Massachusetts voters, in a unique position to either gum up the works or grease the wheels for the Democratic agenda in Washington, appeared to flex their clout in Tuesday's special election, with poll workers reporting a steady stream of voters at the ballot box despite the snow. 

That's a sharp contrast from the lackluster voter interest seen in the December primary. With the general election suddenly competitive and national policymakers fixed on the race due to the implications it could have for Capitol Hill, Massachusetts voters were heading to the polls in droves to try to tip the balance of the race. 

Massachusetts Secretary of State William Galvin is predicting up to half of the state's 4.1 million registered voters could turn out. Polls close at 8 p.m. ET. 

The two candidates, Democrat Martha Coakley and Republican Scott Brown, are far apart on the issues, but even in this heavily Democratic state Brown has built an insurgent campaign, analysts say, by connecting with voters and hammering Coakley as part of the party establishment. The two candidates are vying to fill the seat formerly held by the late Sen. Ted Kennedy

"This is going to be the most significant special election in modern American history if Scott Brown wins," said Larry Sabato, director of the University of Virginia Center for Politics. He predicted a Brown win would buoy every other "long-shot" Republican candidate in the country and add fuel to the party's momentum going into the midterms this fall. 

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More immediately, a Brown win would pose big problems for President Obama's agenda items, not the least of which is health care reform. Brown, should he win, would break the Democrats' 60-vote, filibuster-proof majority, sending Democrats into a scramble to pass the health care bill before he arrives. 

Former Massachusetts Gov. Mitt Romney, the last Republican to lead the Bay State, said the close race -- which was not so close just a few weeks ago -- shows voters are disappointed with the "arrogance" they see in Washington. 

"That kind of attitude, I think, has gotten a lot of people here very, very concerned, and I think it's a sentiment that's growing around the country," Romney told Fox News. "This is big." 

Though Republicans like Romney have occasionally been a political force in state politics, Massachusetts voters have not sent a Republican to represent them in the U.S. Senate since 1972. Every member of the state delegation currently in Washington is a Democrat. 

Democrats outnumber Republicans 3-to-1 in the state -- 37 percent of registered voters are Democrats, 12 percent are Republicans and 51 percent are unaffiliated. Obama won the state by 26 percentage points in the 2008 presidential election. 

Brown's campaign marked an upset just by being as competitive as it is against Coakley's. 

The campaigns have been inundated with help from outside the state. Obama and former President Bill Clinton both came to campaign rallies for Coakley, and Obama appeared in a television ad. 

"Every vote matters, every voice matters," Obama said in the ad. "We need you on Tuesday." 

Sen. Arlen Specter, D-Pa., pitched in by having his campaign team make phone calls to get people out to the polls. According to one Democratic Senatorial Campaign Committee staff member who stayed behind in Washington, it's all hands on deck in the Bay State. 

The National Republican Senatorial Committee in Washington also has "emptied out the building" of staff to send nearly everyone to Massachusetts to help Brown get out the vote. The NRSC reportedly quietly shifted $500,000 to help Brown's campaign in the last two weeks. 

Arizona Sen. John McCain, the 2008 Republican presidential candidate, contacted his extensive and valuable fundraising lists on behalf of Brown last week. Independent tea party organizations are also offering phone banking support to Brown. 

"I came up to help out because of the excitement, we have so many people turning up at our volunteer phone banks we have to turn them away," said one such Republican operative, "Stuff like this is why I got into politics." 

Lt. Gov. Tim Murray noted that the race closed its 15-point gap in recent weeks because of the increased attention but Republicans have typically ran close races in the state despite a 3-1 Democratic to Republican voter registration gap. 

"There's no question about it that this is a horse race," Murray told Fox News, adding that the Massachusetts race has turned national because Americans don't have any other election contests to watch. 

"The eyes of the country are on this race and people from the right and the left are here and involved trying to make a difference," he said. "You can't take any election for granted in Massachusetts, probably, or anywhere around the country these days." 

Indeed, the swift rise of Brown, a relatively low-profile Republican state senator, in his race against the state attorney general has spooked Democrats who had considered the seat one of their most reliable. 

"In Scott Brown we have an irresponsible, homophobic, racist, reactionary, ex-nude model, teabagging supporter of violence against woman and against politicians with whom he disagrees," MSNBC host Keith Olbermann said, echoing the fear chamber that has included several senators making overt reference to the sex act in describing the conservative grassroots tea party movement. 

Kennedy, who died in August, held the post for 47 years. 

Brown has tried to turn Democrats' expectation of an easy win to his advantage, proclaiming, "It's not the Kennedy seat, it's the people's seat." 

On Monday, Brown made another bus tour of the state, shaking hands with Boston Bruins fans at lunchtime and ending his day in his hometown of Wrentham, Mass., before an enthusiastic crowd of supporters, again touting the endorsement of former Red Sox pitcher Curt Schilling. 

"It's us against the machine," he told the group, urging them to vote. "Make sure that we send a message to Washington that business as usual is not how we like to do business." 

Coakley also toured the state, enlisting the aid of top Democrats and making a final pitch to female voters. If she wins, Coakley would be the first woman elected to the Senate from Massachusetts. 

A Suffolk University survey taken Saturday and Sunday showed Brown with double-digit leads in three communities the poll identified as bellwethers: Gardner, Fitchburg and Peabody. But internal statewide polls for both sides showed a dead heat. 

For Brown's staunchest supporters, such as Glen Stump, 47, a software engineer from Andover, Democrats' appeals fell on deaf ears. 

"I hope he can stop this Obamacare legislation," Stump said, using critics' nickname for the health care overhaul bill. "I think it's being run in a completely partisan manner." 

A third candidate, Joseph L. Kennedy, a Libertarian running as an independent, said he's been bombarded with e-mails from Brown supporters urging him to drop out and endorse the Republican. Kennedy, who was polling in the single digits and is no relation to the late senator, said he's staying in. 

Fox News' Trish Turner, Molly Line and Jake Gibson contributed to this report.