If the economy stays the current course, there's a very strong chance that President Barack Obama will be a one-term leader, according to an analysis by global economic consulting firm IHS Global Insight. But there's hope for the Democratic leader yet.

The firm notes that "over the years, statistical attempts to explain and predict U.S. presidential election results have yielded two overarching themes." One of these, the tendency of Americans to vote for incumbents, is good news for Obama. But the other, the tendency of American to vote their pocketbooks, is obviously bad news. And the economic rule, as happened with Jimmy Carter and George H.W. Bush, is powerful enough to trump incumbency rule.

IHS Global Insight Chief U.S. Economist Nigel Gault and Economist Erik Johnson project "just a 43.5% share of the two-party vote for the president, i.e., a heavy defeat" based on the likely state of the economy.

That statement carries with it some pretty serious caveats. One, of course, is the economy. While IHS thinks a major economic rebound is unlikely between now and election time, the writers note that even a perception that the U.S. is out of the worst and heading for recovery might be enough to help Obama.

But the president's biggest help might come from his opponents. "The election equation takes no account of the identity of the candidates -- a Republican opponent lacking broad appeal could tilt the balance back in favor of the president."

Another thing to consider: a Republican opponent lacking appeal with certain elements of the Republican party (whether he or she be too moderate or too conservative) could spawn a third-party run, thus splitting the vote.

The equation used by IHS deals only with the popular vote and has a pretty good success rate. It's erred with Humphrey vs. Nixon and Ford vs. Carter, with the authors noting that Democratic turmoil over Vietnam may have been a factor in the first and Watergate may have been in the second. Interestingly, the equation predicted that Al Gore would win the popular vote.

But aside from voter perception, electability, foreign policy and hapless Republican candidates that aren't accounted for by the equation, what would have to happen for Obama to win this equation and the White House?

"If year-on-year GDP growth were to reach 4.0% in the third quarter of 2012, per-capita income gains could strengthen to just over 3.0% year-on-year and the unemployment rate could fall to 7.5% in the third quarter. Under this scenario, the equation delivers Obama the slightest of victories, with a voting share of 50.01%."

But, note the authors: "It has been more than seven years since year-on-year GDP growth eclipsed 3.9%."