Sen. Bernie Sanders (I-Vt.) has continued to close in on Hillary Clinton -- several national primary polls in the last week have shown his support rising to its highest point of the campaign. Sanders’ polling numbers have climbed since he entered the race, and Clinton's previously substantial lead has dwindled to a 10-point margin in the HuffPost Pollster average.

However, overcoming even a 10-point margin at this stage would be incredibly difficult.

National primary polls are good indicators of the country's overall mood, but often have little bearing on how state primaries play out. While it’s clear that Sanders’ message is catching on with more and more Democrats, he remains far behind Clinton in what really matters: the delegate count.

Either Democratic candidate needs 2,383 delegates to lock down the presidential nomination, and more than half of the primaries and caucuses have already happened. Clinton is leading, with 1,243 pledged delegates to Sanders’ 979. Adding in the “superdelegates” -- those who get to vote for the nominee but aren't bound by a state’s contest -- Clinton surges to 1,712 delegates to Sanders’ 1,008. The superdelegates aren’t limited to their stated preference, though, and could change their minds.

Still, Clinton is leading by 264 pledged delegates, which would be difficult for Sanders to overcome unless he can move a huge number of superdelegates over to his camp. This is where his national standing might come into play: Superdelegates could consider national polls when deciding which candidate to support -- and although Sanders clearly has momentum, he still trails. And Clinton is likely to rack up an even bigger delegate lead before he can close the gap.

The delegate race comes down to what happens in the remaining states. Sanders won big in caucuses over the weekend, but there aren’t many states left where he is expected to do so well.

Wisconsin’s primary is next, and the candidates are running neck-and-neck. But since the Democrats in the state allocate delegates in proportion to the votes they get, a narrow win wouldn’t do much to help Sanders catch up to Clinton’s delegate count -- there’s not that much difference between getting 48 percent of the 96 Wisconsin delegates (48 delegates) and 52 percent (50 delegates). He would need a more definitive win to close the gap with Clinton.

The biggest prize in April is New York, where Sanders currently trails Clinton by 20 points. Sanders has expressed his intent to campaign heavily in his birth state, but the same principle applies, even though there are 291 delegates at stake: He can’t make up the delegate differential with narrow wins.