Barack Obama enters his first presidential debate with Mitt Romney this week apparently winning an election that economic precedent and the weight of political history suggest he should lose.

High unemployment, slow growth and polls showing most Americans think their country is on the wrong track would normally doom his reelection hopes and consign him, in his own words, to a "one-term proposition."

Instead, the president leads national polls and battleground states with multiple paths toward the 270 electoral votes needed to win the White House.

Romney, meanwhile, is sinking and lashing out on everything from the national debt to Libya, desperate to draw blood with time running out before November 6.

"When you look at the economic numbers relative to what the polls are saying, it is hard to reconcile the two," said Paul Harrington of the Center for Labor Markets and Policy at Drexel University.

There are several explanations for Obama's defiance of political gravity, including some shoots of optimism amid the economic gloom, a resourceful campaign and a gaffe-prone opponent.

Obama always reminds voters he inherited an economy in freefall that was shedding 800,000 jobs a month in the darkest fiscal meltdown since the Great Depression of the 1930s.

He has a strong case that he stopped the bleeding and can claim credit for creating five million jobs -- but his record once the crisis passed is more questionable, with the economy now drifting in lethargy.

His answer to Romney's frequent question "are you better off now than four years ago?" is complicated by 8.1 percent unemployment and growth that spurts, then coughs to a halt.

Since the recession ended in 2009, quarterly economic growth has only once hit four percent, and normally dawdles along much slower.

Last week, the government cut growth figures to 1.3 percent for the last quarter, triggering new fears of a slide to recession.

The economy is creating jobs far too slowly to slice the jobless rate -- there were just 96,000 new positions in August. Millions of Americans still have underwater mortgages. Many others have given up looking for work.

No president in more than 70 years has won reelection with the jobless rate above 7.4 percent -- a marker Obama has no chance of reaching.

But the economy, it seems, is not bad enough to spell certain defeat for Obama. It is just good enough to allow a quality campaign and the cut of his character to shape the result.

There are just enough rays of economic hope to give voters some optimism.

Spending and personal consumption have been modestly rising all year. The stock market has been on a tear, boosting pension plans and enhancing economic wellbeing.

The Labor Department this week said it had miscalculated previous job growth, adding 386,000 extra jobs, and allowing Obama to now argue he made five million positions on his watch.

The housing market has finally hit bottom, with home prices up for the third straight month in July.

In a recent NBC News poll, 51 percent said the economy was recovering and some polls now show Obama level with Romney on his biggest liability -- economic management.

Obama may also be lucky in the identity of his foe.

For months, conventional wisdom had it that the election would be a judgment call by voters on Obama's economy.

But it now looks like a referendum on Romney, who has yet to frame a convincing economic narrative.

Obama has succeeded in expanding the campaign from a narrow economic argument into a wider fight over social issues, national security themes and appeals to Hispanics, gays, young voters and women in his political base.

His scorching attack on Romney's venture capitalist past meanwhile left his foe with dangerously negative ratings.

Obama's team "painted Mitt Romney as a corporate raider, somebody who couldn't be trusted to handle the economic challenges, who was not suited to be president," said Melissa Miller, a professor of political science at Bowling Green State University.

The Democratic convention in North Carolina was a three-day tribute to the middle class and popular ex-president Bill Clinton made the economic case for Obama better than the president has ever done himself.

The political ghost of George W. Bush also haunts Romney as Obama links his low-tax, low-regulation opponent with the former president.

Romney's gaffe-strewn campaign has also helped, culminating with the release of a secret video showing him dismiss half the nation as tax-dodging, government-dependent "victims."

Conversely, Harrington said, Obama's messaging has been "terrific" and "Romney just has not counter-punched."

The US electoral map might also save Obama.

A case in point: Ohio. Unemployment peaked at 10.6 percent, but has now dipped to 7.2 percent. The auto industry bailout that Obama championed may now be paying him back with a political boost in the state.

Other key states like Virginia and Iowa have also outperformed the wider economy.

Still, five weeks from election day, it is too early to conclude the economy does not have a sting in its tail.

A stellar debate performance by Romney, and a poor monthly jobs report on Friday, could fuel a comeback narrative for the Republican.

Obama will also hope Europe's latest meltdown will wait for November 7.