Voting in the Democratic primary may be more than half over — but national polls of the party's voters are now closer than ever.

The Huffington Post's polling average currently shows Bernie Sanders just 2.5 percentage points behind Hillary Clinton among Democratic voters, which is his best performance ever. Remember, he started the campaign more than 50 points behind Clinton, as you can see below:

Back in February, shortly after Sanders crushed Clinton in New Hampshire, one Fox News poll put him ahead by 2 points among Democrats. She then proceeded to clobber him in several major statewide victories, accumulating a delegate lead that now looks virtually insurmountable.

But now things appear to have tightened again. Most recent polls do still show Clinton ahead of Sanders, but three conducted in the past few weeks have shown Sanders narrowly on top.

What do these polls say about the state of the race?

There's one way of looking at these polls and dismissing them as irrelevant to the actual race: After all, the primary is conducted on a state-by-state basis, and voters in more than half of the country have already headed to the ballot box.

"I don't think it predicts what is going to happen in the next states," says pollster J. Ann Selzer, emphasizing that the statewide delegate contest is what matters most in determining the nominee. "The national average has historically been meaningless … it's kind of interesting, but it's not all that meaningful."

For instance, in 2008 Clinton significantly outpolled Barack Obama in national Democratic polling several times, even after he had effectively won the race.

As late as early May 2008, two polls put Clinton 7 points ahead of Obama. Clinton didn't win the nomination simply because she was doing better in some national Democratic polling.

All of this, however, shouldn't take away from the topline result — even though the political world thinks the race is over and Clinton is overwhelmingly likely to be the nominee, the Democratic Party's rank and file still appears to be about equally split between Sanders and Clinton.

Indeed, some recent polls of big states like California, Pennsylvania, and New York — states Clinton was supposed to be favored in — show Sanders closer to her than ever before.

Democratic delegate rules still make it extremely difficult for Sanders to mount a comeback at this point. But he's pulled off some big surprises before. We'll see if he can manage to do so again.