The Massachusetts seat vacated by late Sen. Ted Kennedy has become the focus of national attention — and liberal anxiety — as the rapidly changing race between Democrat Martha Coakley and Republican Scott Brown (whose victory could kill the health-care reform bill) comes to a head Tuesday. Here, a concise guide to the candidates, the issues and what Tuesday's vote means for our health-care system and the future of Obama's presidency. (Watch top political pundits weigh in on this "referendum" in THE WEEK's newest Sunday Talk Show Briefing)

Why is this election so pivotal?
Democrats, who've controlled this seat for 46 years, were counting on an easy victory to ensure passage of the health-care reform bill. Instead, the election has blown up into a "national referendum" on Obama's health-care and economic policies.

Who's favored to win?
As of Monday night, the race is leaning far in Brown's favor: According to’s latest averaging of independent polls, Brown holds a 3-to-1 edge over Coakley, who once led by a 29 percent margin. Although the Wall Street Journal points out that predicting turn-out is dodgy with special elections like this, one poll shows that 89 percent of Republicans are "very excited" about the race, while only 68 percent of independents (half the state's voting population) and 63 of Democrats describe themselves that way.

What are Scott Brown's credentials?
A Wakefield, Mass., native, Scott Brown, 50, joined the Army National Guard at 19, and currently serves as the Army Guard's leading defense lawyer. He’s also served in the Massachusetts State Senate since 1992. Brown has campaigned as a pick-up-truck-driving populist, denouncing the health-care-reform bill, while supporting smaller government, lower taxes, national debt reduction, a "strong military," and a "vigorous homeland defense.” He’s endorsed by Republicans, Tea Party members, and high-profile figures, including Sen. John McCain, Karl Rove, and former Boston Red Sox pitcher Curt Shilling. For more on Scott Brown, click here.

Why was Martha Coakley expected to win?
This Pittsfield, Mass., native, 56, has worked in Massachusetts government for 20 years, and served as its Attorney General since 2007, the first woman to do so. A classic liberal, Coakley supports health care reform and equal rights; tackling the economic crisis and sustainable energy are among her top concerns. She is widely supported across the state by dozens of labor unions, women's groups, various police organizations and the Gay & Lesbian Political Caucus. For more on Martha Coakley, click here.

How do the two stack up against each other on specific issues?
For a head-to-head comparison, click here.

How did Brown overcome Coakley?
Aggressive campaigning by Scott Brown, missteps by Martha Coakley, and shifting voter attitudes to President Obama's agenda: “Shoo-in” Coakley drastically cut back on campaign appearances, says Glen Johnson in the Associated Press, while Brown's campaign was unleashing an "ad war." Coakley further erred by saying that the Taliban "are gone" from Afghanistan and declaring that Catholics "probably shouldn't work in emergency rooms" because their religion dictates that birth control is a sin. Meanwhile, anti-Coakley organizations such as the National Republican Trust political action committee and Tea Party Express flooded the state with money to support of Brown’s relentless campaign.

What does a Brown win mean for health-care reform?
"If Scott Brown wins,” Democratic Rep. Barney Frank told the Associated Press, “it'll kill the health bill." Democrats will lose their filibuster-proof 60-seat majority in the Senate — opening the door for Brown to cast the deciding vote against the legislation. The Democrats do have other options: The party’s "most likely" gambit, says the AP's Charles Babington, would be to avoid a second Senate vote altogether — a "highly problematic," inevitably controversial, move that would require all House Democrats to approve the Senate's version of the bill. The Democrats could also attempt to orchestrate a vote before Brown takes office (unconstitutional, say Republican attorneys).

How would a Brown win affect Obama's larger agenda?
It could signal a nationwide political mood change, sending “a chilling message to all Democratic candidates on the ballot in November," says S.A. Miller in The Washington Times, and further jeopardizing the Democrats' majority in Congress. Even Obama seems to agree: "Understand what's at stake here, Massachusetts," the president said at a last-minute campaign rally for Martha Coakley in Boston on Sunday. This is about “whether we're going forwards or backwards."


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