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Analysis from ABC News Pollster Gary Langer:

It's hard to overstate how important the unemployment rate is to Barack Obama's re-election prospects. Not just the number, but its trajectory, and the closely related public perception of the condition of the economy overall.

Unemployment was 7.8 percent when Obama took office; his popularity dropped as it rose (reaching a high of 10.1 percent in October 2009).  But as unemployment has eased in the past few months, consumer confidence has improved to its best in nearly six months, and the president's job approval advanced to 49 percent in recent ABC News/ Washington Post and CNN polls - his best in 9 months, excepting a brief bin Laden bounce.

For context, consider Ronald Reagan. In late 1982 unemployment hit 10.8 percent; shortly thereafter Reagan's job approval rating bottomed out at 42 percent, the same as Obama's low this past fall. By January 1984, unemployment was down to 8.0 percent, a half-point from today's level. By November 1984, it was down to 7.2. percent, and Reagan easily was re-elected.

As the 2012 election season unfolds, there may be no better number to watch.

Read more about presidents and unemployment rates.