‘WHERE IS THE WAVE?’…. Arguably the most important election yesterday wasn’t a primary race, but rather, the congressional special election in Pennsylvania’s 12th — a contest to fill the vacancy left by the late Rep. Jack Murtha (D).

Observers in both parties considered the race something of a bellwether. Democrats ran Mark Critz, a former Murtha staffer, against businessman Tim Burns, who touted his “outsider” status and association with the right-wing Tea Party “movement.”

It was the race Republicans felt like they had to win, and the RNC boasted repeatedly that a victory in Pennsylvania’s 12th would foretell significant gains in the midterms. It didn’t work out the way they’d hoped.

[T]he special election in Southwestern Pennsylvania suggested that Democrats were able to score victories in this challenging political environment. Mark Critz, a former aide to Mr. Murtha, defeated Tim Burns, a Republican businessman. With 95 percent of precincts reporting, Mr. Critz had 53 percent, compared with 45 percent for Mr. Burns.

Though Democrats dominate in the district, its voters are blue-collar conservatives and it is exactly the type of swing district carried by Senator John McCain in the 2008 presidential race that Republicans must win if they are to reach their goal of taking control of the House in November. The loss dealt a blow to Republicans, who have been raising expectations for the fall.

“If you can’t win a seat that is trending Republican in a year like this, then where is the wave?” asked Tom Davis, a former Republican congressman from Virginia, who said Republicans will need to examine what went wrong.

That’s hardly an unreasonable question.

This is the only district in the country that backed Kerry in 2004, but McCain in 2008, suggesting it was trending heavily in the GOP’s direction. If there’s going to be a backlash against Dems right now, this should be the place to find it. Indeed, it was the bulk of Burns’ platform — he specifically ran against Washington, Speaker Pelosi, and the Obama presidency, a pitch Republicans intend to duplicate in other competitive districts through the fall.

And while polls showed Burns with a slight edge going into the election, Critz nevertheless won fairly easily.

Marc Ambinder noted yesterday, long before the polls even closed, “If the Republican doesn’t [win], I think us pundits in Washington are going to have to revise our thinking about whether this is a wave election year for Republicans.”

Once the results were in, Politico added that “Republicans failed spectacularly, losing on a level playing field where, in this favorable environment, they should have run roughshod over the opposition…. The district itself couldn’t have been more primed for a Republican victory.”

In fairness, there are some relevant caveats here. There was a Democratic Senate primary, which may have boosted turnout a bit in Critz’s favor. For that matter, Critz didn’t exactly run as a bold progressive — he touted his opposition, for example, to the Affordable Care Act and cap-and-trade.

But Republicans decided weeks ago that this is the kind of district that they’ll have to win this year. RNC Political Director Gentry Collins conceded yesterday that this is “exactly the kind of seat that we have to win.” Last week, Newt Gingrich said, “This year, we have mobilized millions of people from all over the country, and they are ready to take back this country. It’s going to start right here, right now in” Pennsylvania’s 12th.

They lost by eight points. It raises uncomfortable questions for Republican strategists, who’ve done nothing but raise expectations about what’s possible in November.

For those keeping score, there have been seven special elections for U.S. House seats since the president’s inauguration 16 months ago: NY20, IL5, CA32, CA10, NY23, FL19, and PA12. Democrats have won all seven.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.