Gallup reports this morning that its “economic confidence” index is up sharply over the last several months. That number, which takes into account Americans’ ratings of current economic conditions and their overall economic outlook, is now at its highest point since last May.

The overall numbers are still not very good. But confidence as measured by Gallup has fully recovered from a summer slump, and is rallying to close to its post-recession highs, and is well above the levels from George W. Bush’s last year in office. For now, anyway.

Gallup’s finding matches a similar indicator in a recent Washington Post poll, which found that there’s been a net 18 point swing in favor of the idea that the economy is improving.

So it’s worth remembering: When it comes to economic indicators and presidential elections, the evidence is strong that what matters are election year trends — the public’s sense of which way the economy is moving — not overall four-year performances or even absolute levels of economic strength.

In other words, come Election Day 2012, if things are improving, or if the public perceives things to be improving, the president is likely to be re-elected. Fairly or unfairly, the political science literature shows that voters don’t seem to hold a president’s economic performance earlier in his term against him. As long as things are getting better, even if they’re still overall quite bad, voters tend to support re-election.

That’s why Ronald Reagan was able to win a massive landslide even though unemployment was still relatively high in 1984. (This dynamic may have also been the source of Al Gore’s problems in 2000; even though the economy was still in excellent shape, some indicators had already turned negative in advance of the 2001 recession.)

Of course, confidence numbers, and more importantly economic growth, have rallied before during the Obama presidency only to sag again. But today’s numbers are a reminder that while it’s far too late for a great four-year economic performance (regardless of whose fault that might be), there’s still time for the economy to make Obama’s re-election a lot easier than most people think it will be.