Late last week, we published a chart detailing the unemployment trend line since President Obama took office.

The chart above may well represent the best chance President Obama has at a second term. We’ve long maintained that a president’s stewardship of the economy — particularly in tough times — is judged more by the direction in which the unemployment rate is headed than what the actual number is in the runup to an election.

After we put out that chart, we heard from lots of people — Democrats, mostly — who pointed us to a similar chart tracking the unemployment trend line during Ronald Reagan’s 1984 re-election race.

It’s become a Washington parlor game to compare Obama’s presidency to others who held the office — Lincoln! Clinton! — but it’s long been obvious that Reagan’s 1984 race is the closest analog to what Obama is currently going through.

A faltering economy had hamstrung Reagan’s party in the 1982 midterm election, causing across-the-board losses. (Sound familiar?) Reagan began his re-election race with unemployment above 10 percent but by the time he stood for re-election that number had dipped below eight percent.

While a 7.4 percent unemployment rate was far from ideal for a president seeking a second term, the trend line allowed Reagan to make the case that his policies were beginning to turn things around and that it made no sense to change horses in midstream. Voters agreed; he carried 49 states.

Obama’s political team — as well as virtually every economist in the country — acknowledges that there is almost no chance that unemployment will dip below eight percent before next fall.

That reality means his best hope lies in an incremental drop in the unemployment rate so that he can make the “progress is being made” case to the public.

In short, Obama needs to duplicate the second chart above. Do that and his chances of winning a second term increase measurably.