It’s quarter after 10 on a chilly Saturday morning in late October, and Rep. Scott Murphy’s people are a little peeved. There are only 10 days until the voters of New York’s 20th Congressional District go to the polls to decide whether Murphy, the hulking, fair-haired, Harvard-educated Democrat and former entrepreneur who emerged from obscurity to defeat prominent state Assemblyman Jim Tedisco in the March 31, 2009, special election to replace Kirsten Gillibrand, gets to return to Washington.

The race is close. Murphy’s private campaign polls give him a narrow lead; his Republican rival, Chris Gibson, has leaked internals that show Murphy trailing. So when the congressman emerges from his dented Honda minivan at the Burnt Hills Farmers’ Market to find nothing but a few Spartan stands set up in a supermarket parking lot—and not a single shopper shopping—his staff immediately starts to revise his schedule. “We’re not going to stick around a whole lot longer,” says one aide. “Not a lot of people here.”

But Murphy presses on. For the next half hour, he does what politicians do. He discusses goat cheese with a farmer wearing a Marlboro belt buckle. He purchases “home-growed popcorn” for $2. And he tells anyone who’ll listen about his work on the House Agriculture Committee. All told, Murphy talks to no more than 10 constituents at the “event”; whether any of them will turn out for him on Nov. 2 is a mystery. But the message to his staff is clear: we’re not taking a single vote for granted.

Murphy was right to be concerned. This week, he lost his reelection bid to Gibson, a retired Army colonel, by a dismal 11 percentage points—one droplet in the historic wave that generated net Republican gains of seven or eight seats in the Senate and roughly 65 seats in the House. As recently as September, Murphy looked like a winner. A poll by Siena College of Loudenville, N.Y. showed him leading Gibson by 17 points, 54 percent to 37 percent; he was ahead 58 percent to 30 percent among independents, 58 percent to 32 percent among women, and 58 percent to 36 percent among voters under 55. But on Oct. 26, Siena released another survey showing that over the previous month and a half of the campaign, Murphy’s support had collapsed. In Siena’s final sounding, voters in NY-20 preferred Gibson 51 percent to 42, a nine-point margin that mirrored the eventual outcome of the race. Women (49–42), independents (49–42), and younger voters (55–37) had all defected to the Republican. In the end, it didn’t matter that Murphy had outraised Gibson nearly 4–1 or that he’d avoided making any serious mistakes. He lost anyway.

What happened? The answer isn’t particularly sexy—or particularly simple. But it is important. In many ways, Murphy was 2010’s quintessential endangered Democrat, a centrist rookie in a rather Republican district who was swept into Washington during one of the left’s recent electoral routs. And because he’s so typical, his loss says a lot about why the Democratic Party will soon have to surrender control of the House.

The first reason Murphy isn’t returning to Congress is that he’s a Democrat. Much has been made over the past few months of the electorate’s alleged “anti-incumbent” or “anti-establishment” mood. But like Murphy, many of the Democratic members who lost on Tuesday simply weren’t on Capitol Hill long enough to be seen as “creatures of Washington”; they arrived in 2006, 2008, or 2009 and were only beginning to learn how to navigate the halls of power. The real problem was the way they voted on big-ticket Democratic legislation like the stimulus, cap-and-trade, and health-insurance reform, and the way those votes were eventually used against them.

Murphy is a prime example. Delivering his stump speech at the Greenwich Elks Lodge in Greenwich, N.Y., the Saturday before the election, the congressman performed a tricky two-step: distancing himself from Washington (a prerequisite for disgruntled voters) without disavowing the work he’s done there (which would be a sure sign of hypocrisy, i.e., “politics as usual”). Murphy had previously attracted some national attention for an ad touting his support of health-care reform, but at the Elks Hall, he was careful to note that he’d opposed the original, less thrifty House version and that he would push to revise the law if awarded another term in Congress. And he hammered away at his campaign’s main line of argument: that he was a “businessman” who’d created “more than 1,000 jobs” in the area, not a career politician or doctrinaire Democrat. In fact, as he pointed out, the National Journal had characterized his voting record as one of the 10 most moderate in the House. Even the National Rifle Association had endorsed his bid.

But despite his deviations from Democratic orthodoxy, Murphy supported the two biggest items on Nancy Pelosi’s agenda: health-care reform and cap-and-trade legislation. They were his downfall. Once Gibson started slamming those votes—sometime between the first Siena poll, when 65 percent of respondents were unfamiliar with the Republican candidate, and the second, when that number had plummeted to 24 percent—voters disgruntled with the direction of the country (read: almost everyone) decided that Murphy, however unorthodox, had played enough of a part in determining that direction not to deserve another term. Some of them may have voted against the policies, but most of them were simply voting against the status quo. In a legislative sense, Pelosi’s skill at rounding up “ayes” on controversial bills has served the Democratic Party well: the 111th Congress was the most productive in recent memory. But on Election Day, her successes made it difficult for vulnerable Democrats to claim that they’d bring about more change than their opponents.

The rest of Murphy’s hurdles were more structural than personal. For starters, Republicans have a massive registration advantage over Democrats in New York’s 20th Congressional District, perhaps the most conservative in the state. In late October, Siena pegged the likely electorate at 41 percent Republican, 29 independent or “other,” and only 27 percent Democratic. The inherently conservative character of Murphy’s largely rural and exurban district was further skewed during the last round of redistricting, in 2002, after which John Sweeney, the GOP congressman then in office, reportedly boasted that “no Republican can ever lose” the 20th. Today, roughly a dozen colleges sit within a few miles of its borders. Making matters worse: Murphy was elected last time by a mere 726 votes—the slimmest margin of the entire 2008–09 cycle. In every way, he was skating on thin ice.

Unfortunately for Democrats, Murphy wasn’t the exception—he was the rule. The majority of Tuesday’s Democratic victims were also recently minted representatives from hostile districts, precisely the sorts of candidates who tend to suffer in wave elections. As Jonathan Chait has explained, “the more seats you hold, the deeper into hostile territory you’re stretched, and the easier it is to lose seats.” Democrats, in other words, were already stretched to the limit. That's a major reason why Murphy lost on Tuesday, and why the Blue Dog caucus—the House’s most prominent gang of moderate-to-conservative Democrats—was cut in half.

The final nail in Murphy's coffin was money, or, more specifically, the kind of money (unlimited, anonymously donated cash from outside interest groups) that was legalized by the Supreme Court’s recent Citizens United decision. On Oct. 15, Karl Rove’s behemoth American Crossroads organization made Murphy its first target in the House, launching a $447,366, 11th-hour ad campaign against the incumbent congressman. Related groups like the 60 Plus Association, Revere America, Americans for Prosperity, and the Tea Party Express had already invested hundreds of thousands of dollars in the race. All told, independent groups spent more than $2.8 million dollars to defeat Murphy, more than they dropped on any other Democratic congressman. The resulting barrage of negative ads largely explains why Murphy’s favorables slipped from 56 percent in September to 45 percent in October, and why his unfavorables skyrocketed from 27 percent to 45 percent over the same period of time. A former banker and venture capitalist, Murphy had the connections to fight back, raising $4.8 million in all. But it wasn’t enough. For other, less prosperous candidates, the sudden flood of outside money was even harder to withstand.

In his concession speech Tuesday night, Murphy said he had “no regrets.” “We always knew it was going to be competitive,” he added. “We had a credible opponent.” Still, he must have been frustrated: with voters for failing to acknowledge his moderate record, with his Republican predecessors for carving out such a hostile district, with Rove and Co. for spending him into the ground. Multiply that frustration by 65 or so and you’ll get some sense of how the rest of the Democratic Party is feeling right about now.