Democrats spent Wednesday trying to explain away a disappointing loss in a Florida special congressional election that they had been expected to win.

“The takeaway from the special in Florida is that Democrats will need to invest heavily in a national field program in order to win in November. Nearly 50,000 fewer people voted in the special than in the 2010 general election, a 21% drop off,” officials at the Democratic Senatorial Campaign Committee (DSCC) wrote in their daily morning memo.

Already facing a difficult task in reclaiming the House majority, some Democrats said the loss in a district that President Obama won twice should serve as a warning sign that the party’s voter-turnout operation is rusty and is endangering the Democratic majority in the Senate.

In private meetings, House Minority Leader Nancy Pelosi (D-Calif.) and top lieutenants told lawmakers that the race would not define the midterm elections in November, also pinning the defeat on a dismal turnout effort, according to aides and lawmakers in the meetings.

“It’s a disappointment, I won’t pretend it isn’t,” said Rep. Gerald E. Connolly (D-Va.), exiting a House Democratic Caucus meeting that Pelosi tried to keep focused on staying the course toward the midterms. “It’s a loss, it’s a disappointment. It’s not the end of the world. And I don’t know that it tells you a lot about the complexion of the election in November of this year.”

Republicans openly mocked the Democratic effort to explain the results.

“It’s very significant, by any objective standard,” Senate Minority Leader Mitch McConnell (R-Ky.) said in an interview, citing the Republican candidate David Jolly’s first-time candidacy and record as a Washington lobbyist as reasons he should have been defeated. Democrats fielded a former statewide official and spent more money than the GOP, while Jolly focused relentlessly on Obama’s handling of the Affordable Care Act’s implementation.

“It’s an indication the American people in a swing district, or arguably a blue district, might want to go in a different direction,” McConnell said.

The Jolly victory came just days after GOP strategists were privately mocking the quality of his campaign. It put Democrats deeply on the defensive because their candidate, 2010 gubernatorial nominee Alex Sink, ran what party officials considered a textbook campaign by pledging — on camera in TV ads that ran heavily — that she would work to fix parts of the health-care law but not entirely repeal it.

Her campaign message is expected to be repeated over and over by Democratic challengers in GOP districts throughout the nation, as well as by four key Senate incumbents who voted for the 2010 health-care measure. The fate of those four senators, all running in states Obama lost in 2012, is likely to determine the balance of power in the Senate, where GOP candidates are clear favorites in at least two states and would need four more to claim the majority.

The question facing Democrats is whether they can energize enough of their voters for the midterm election. In a series of events with Democratic activists and donors, Obama has sounded the alarm and warned that the final two years in office would be imperiled with a Republican-controlled Senate — a refrain with little to show for it so far. The DSCC has already launched its own $60 million program to try to turn out voters this fall, a particularly key need in several Senate races in states where Obama did not actively compete in 2012.

In a conference call with reporters, Rep. Steve Israel (N.Y.), chairman of the Democratic Congressional Campaign Committee, and a Democratic pollster contended that the fix-it message worked to neutralize the negative effect of the health-care law.

But they said that the district skewed as much as 13 percentage points in the GOP’s favor in this election, a disparity that Sink could not overcome.

“This was a tough loss because it was such a close loss,” said Israel, who turned to a baseball analogy to explain his thinking. “I’m a Mets fan. I’d rather lose by 13-0 than 13-11, and we got it to 13-11,” he said.

Left unanswered by Democrats is precisely why their voters were so unwilling to turn out for Sink — given that they lauded her Wednesday as a strong candidate with a good message and plenty of campaign money.

Israel is already recruiting her to run again in the normally timed November election. Pinellas County, in which most of the district sits, was one of the key battlegrounds in Obama’s presidential campaigns, meaning the Democrats had ample experience pulling out voters in the region.

In the 2012 presidential election, more than 300,000 people voted in the Tampa Bay peninsula district, in which the late C.W. “Bill” Young easily won a 22nd term; in 2010, a bad year for Democrats, about 230,000 cast ballots, and just 180,000 voted in the Jolly-Sink race.

If the candidate, her message and her finances were up to the task, some Democratic advisers privately wondered whether voters had reached a sense of general malaise toward Obama, not his agenda, and whether Republicans were now perceived as the agents of change.

An NBC News/Wall Street Journal poll released Wednesday showed that 65 percent of voters believe the nation is headed on the “wrong track” while just 26 percent believe things are “headed in the right direction,” marking almost nine straight months in which the “wrong track” figure has been more than 60 percent.

In addition, there were trouble signs for the Democratic message. Voters were asked whether they would be more likely to vote for a candidate who “supports fixing and keeping the health-care reform law,” and by 45 percent to 42 percent, voters favored the Democratic approach.

But voters were also asked whether they would be more likely to vote for a candidate who “supports repealing the health-care reform law,” and by a 47 percent to 32 percent margin, voters backed the Republican position. That suggests that the repeal message, at this moment, may create a more energetic response.

Key Democrats said they were not concerned about the GOP fixation on the health-care law, believing that they can spend the next few months explaining the issue to the public and that voters this fall will cast their ballots on a wide array of issues.

“It’s a losing strategy,” Sen. Mary Landrieu (D-La.), one of the top targets this fall, said of the repeal campaign, “and it will not work.”

One thing that did work for Republicans in this campaign was a more organized effort by conservative groups. Overall, Sink and her liberal allies spent nearly $1 million more on television ads than Jolly and his conservative backers, but the conservative groups organized their ad purchases and their messages much better than in previous campaigns.

The Republican groups hit the airwaves with complementary messages and avoided stepping on each other’s toes or doubling up unnecessarily. According to GOP sources, the Republican organizations spaced out their buys so there was coverage during the whole campaign.

Not everyone was up at the same time. “It’s a page from our playbook,” said one Democrat with an eye on the race, who spoke on the condition of anonymity to provide a candid assessment.

Scott Clement, Wesley Lowery and Ed O’Keefe contributed to this report.