Because recent polls show the Republican Brown leading.
How is this happening? Well, Coakley has run a bad campaign, and Brown has run a good one. Yes. But there's a deeper reason the race is close, which ought to have all Democratic candidates up for reelection this year scared of getting "Coakleyed."
Put simply, the Democrats are the party in power, and the public is unhappy about the state of the country. So the Democrats will suffer. Big elections are usually referendums on the party in power. That's why as early as 2006 everyone knew that a Democrat would be elected president in 2008. It almost didn't matter who ran, because George W. Bush and his brand of Republicanism were that disliked.
Of course one way for Democrats to improve their position before the 2010 midterms would be to improve the economy in ways that are readily apparent to the majority of Americans and then take credit for it. (The 10% of the country who are unemployed are waiting.)
The other way for the party in power to succeed in bad times is to disassociate itself from the status quo. They have to say essentially, "Yeah, times suck, and we are the government. But there's a bigger, darker power that we're fighting on your behalf." When Republicans have done this in the past, it's been kind of silly, because they have to make the "bigger, darker power" some vague cultural force, like the "liberal cultural elite" or the "homosexual agenda" or something. (That reminds me: A friend once told me he knew that by voting Republican he was voting against his own economic interests, but he said it was a sacrifice he was making for a higher purpose.)
Democrats in power during tough times really do have a bigger, darker force they can point to: corporate power. The combined influence of Wall Street, the business lobby, and an obstructionist Republicans minority really can outweigh the power of a Democratic Congress and White House. (Especially since Wall Street's political influence is not limited to just the Republican Party.)
To win in 2010 and 2012, Democrats need to pick a fight with the Corporatocracy and paint Republican candidates as corporate lackeys. What would this look like?
Here's a start. "We want the taxpayers' money back--all of it," President Obama says as he proposes a fee on banks with more than $50 billion in assets, to recover money spent bailing out big financial institutions. "And we're going to collect every dime." The details of the plan are not as important as the way the president frames the fight. He talks about "the banks and the politicians who curry their favor" launching "a massive lobbying campaign against common-sense rules to protect consumers."
The president has picked a fight with the big banks, and the Republicans have rushed to the banks' side. The public needs to see this fight raging across the board on a variety of issues--a Democratic-led government battling a greedy, reckless corporate plutocracy and its Republican foot soldiers. Only then does it make sense that a Democratic Congress and tough economic times means we need more Democrats in Congress. The president and Congressional leaders need to pick more fights like the bank tax. And they've got to do it in ways that are bold and visible to the public. Or else, over the next few Novembers, they could all be Coakleyed.