Oct. 5, 2012 -- Mitt Romney surprised President Obama with a dynamic debate performance Wednesday night, but he's been upstaged today by another October shocker as the unemployment rate plunged from 8.1 to 7.8 percent, its lowest since Obama took office in 2009.

The Labor Department report has triggered a mixture of cautious optimism from Democrats, who were looking for some good news after Obama's disappointing performance at the debate, and disbelief bordering on suspicion from Republicans and business leaders, some of them attempting to cast doubt on the veracity of the figures.

"This morning we found out the unemployment rate fell to its lowest rate since I took office," an energized president said during a rally in Fairfax, Va. "More Americans entered the work force, more people are getting jobs.

"It's a reminder this country has come too far to turn back now," he said.

Romney, also in Virginia, joined a chorus of Republican leaders questioning whether the report could be taken as an accurate indicator of economic progress.

"The reason it's come down this year is primarily due to the fact that more and more people have just stopped looking for work," he said. "And if you just dropped out of the work force, if you just give up and say look I can't go back to work I'm just going to stay home, if you just drop out all together why you're not longer part of the employment statistics."

Others employed conspiracy theories to challenge the significance of the latest jobs report.

"It appears that Obama has hired infamous Iraqi Information Minister Baghdad Bob to calculate the unemployment rate. Anyone who takes this unemployment report serious is either naïve or a paid Obama campaign adviser," Americans for Limited Government, a conservative group, said in a statement this morning.

Baghdad Bob was known for claiming American forces were being routed in battle right up to the day U.S. troops occupied Baghdad.

"Unbelievable jobs numbers," tweeted former General Electric CEO Jack Welch. "These Chicago guys (Obama campaign headquarters are based in Chicago) will do anything… can't debate so change numbers."

The Romney camp was less colorful in its response, but joined a chorus of Republican leaders questioning whether the report could be taken as an accurate indicator of economic progress.

"This is not what a real recovery looks like," the Republican's campaign emailed about an hour after the report went public. "If not for all the people who have simply dropped out of the labor force, the real unemployment rate would be closer to 11 percent."

House Majority Leader Eric Cantor, R-Va., conceded that the "report offered some encouraging news," but it still "isn't good enough."

Top Democrats have been mostly quiet; careful not to be seen celebrating in what remains an unforgiving economic climate for many Americans, especially those in a number of swing states with unemployment rates routinely exceeding the national average.

"Too many middle class families that are still struggling to pay the bills," Obama said. "They were struggling long before the crisis hit. but today's news certainly is not an excuse to try to talk down the economy to score a few political points."

Nancy Pelosi, the Democratic House minority leader, was similarly careful.

"Today's jobs report marks the lowest unemployment rate in four years," she said in a statement. "But we have more work to do. Because of President Obama's leadership on the economy, we avoided another depression and now have registered 31 straight months of private sector job growth… The unemployment rate is lower than when he took office."

The Labor Department will issue one more jobs report before the election, unveiling November figures on election eve Nov. 2.

Not all Republicans are dismissing today's news. Florida Gov. Rick Scott seemed pleased enough, sharing in a tweet that "Tampa-St.Pete.-Clearwater and Miami area experienced largest unemployment rate declines in country."

The Complicated Science of Unemployment Rates

Calculating the unemployment rate can be a tricky business. "Participation" this past month came in at 63.6 percent, the lowest in more than two decades. People who do not participate, who have become too discouraged to look for work, are excluded from Labor Department consideration.

As Guy LeBas from Janney Montgomery Scott, a Philadelphia brokerage firm, explains: "The household survey has become an increasingly misrepresentative labor market indicator, mostly resulting from fairly sharp changes in the composition and size of the labor force. For September, the unemployment rate slid .4 percent to 7.8 percent, an amazingly large decline. The big drop was the combined result of a reduction in labor force participation… and a bizarrely big increase in household employment of 873K."

The "bizarrely" large increase was in good measure the result of upward revisions from statistics released in July and August.