WASHINGTON » The drop in the unemployment rate last month opens up a new front in the presidential campaign, with the White House getting a first big opportunity to define an improving trend in the economy and Republicans emphasizing that conditions still remain unacceptably bad.

Within minutes of the government’s announcement that the jobless rate had declined to 8.6 percent in November from 9 percent a month earlier, Mitt Romney blasted out a statement noting that unemployment had remained above 8 percent throughout the 34 months of President Barack Obama’s tenure in office, "the longest such spell since the Great Depression."

Making no mention that the jobless rate is now down 1.5 percentage points from its peak two years ago, Romney added: "The Obama administration may have come to accept such a high level of joblessness as the new normal. I will never accept it."

A few hours later, the president cited the growth in jobs without ever mentioning the level of unemployment. "Despite some strong headwinds this year, the American economy has now created, in the private sector, jobs for the past 21 months in a row," Obama said, appearing in Washington alongside former President Bill Clinton, as good a visual symbol as any of prosperity under a Democratic administration.

The differing responses highlight a big question as the primary seasons draws near: Which is more politically powerful, a positive trend in job growth or the absolute level of unemployment?

The ability of the two parties to persuade voters to look at the situation their way — for Democrats, that the country is making progress and the economic medicine is working, for Republicans that no incremental improvements can eradicate the failure of Obama’s economic leadership — is shaping up as central to the 2012 campaign.

Voters appear to judge the economy by a variety of measures other than unemployment, from job creation to income growth, as well as by a qualitative sense of well-being or lack of it. In any case, there is no assurance that joblessness will continue to drop, or that the financial crisis in Europe will not derail any hope the White House has of being able to sustain the argument that the worst is behind us.

The global uncertainties have some Democrats concerned about overplaying the progress theme, out of concern that the economy could be rocked by events outside the control of the president or anyone else in the United States. As a result, the White House is sure to hedge its bets somewhat, continuing to hammer away at themes like economic fairness and Republican obstructionism. "While the U.S. economy is healing, the world economy continues to be in a fragile state and all economies are linked through trade and finance," said Alan Krueger, chairman of the White House’s Council of Economic Advisers.

Should major economic trouble hit, Obama’s team wants to have built the case for the argument that Democrats, more than Republicans, would better protect the middle class. No president has been re-elected since the 1930s with an unemployment rate at today’s level.

But if the unemployment rate continues to move downward even modestly next year, Obama and his team will be able to take some comfort from history. Under this administration, the peak in unemployment was a little over two years ago, at 10.1 percent. It fell briefly below 9 percent early this year, but has not been as low as 8.6 percent since March 2009. When Obama took office in January 2009 the rate was 7.8 percent, and rising fast.

Democrats are looking to 1984, when President Ronald Reagan won re-election after the rate peaked at 10.8 in late 1982, fell to 8.5 percent a year from Election Day — about where it is now — and declined to 7.4 percent by the time voters went to the polls.

Obama’s own forecast holds little prospect of a continued drop of the scale seen in 1984; the White House has projected that joblessness would average 9 percent next year. And this most recent November drop creates the risk that any backsliding next year would be cast as evidence that things are getting worse again.

If the economy is perceived to be deteriorating in the first half of an election year, it may be very difficult for a sitting president to change voter sentiment. In 1992, the last election to revolve around the economy, President George H.W. Bush was defeated in his re-election bid as the unemployment rate rose to a high of 7.8 percent in June before easing back to 7.3 percent by Election Day.

If nothing else, the positive news on employment Friday came at a moment when Democrats were gaining confidence that they had found an economic message that was resonating with voters, leaving Republicans feeling a bit off balance after a year in which they have driven the agenda in Washington.

Republicans on Capitol Hill were showing signs of division over whether to go along with Obama’s demand for an extension of the payroll tax deduction. Obama, in turn, turned up the pressure on Republicans to go along before adjourning for Christmas.

But on the campaign trail, Obama’s potential Republican challengers were ceding no ground. Newt Gingrich called Friday’s employment report "yet another landmark in the Obama jobs crisis." The key statistic, Gingrich said, was the more than 300,000 Americans who had dropped out of the labor force.

© 2011 The New York Times Company