Story highlights Clinton leads Sanders, 50% to 48%, in the national Democratic race, a new poll shows

Clinton's national lead has declined from one month ago

(CNN) Hillary Clinton holds just a two-point lead over Vermont Sen. Bernie Sanders nationally in the Democratic presidential race, a new poll shows.

An NBC News/Wall Street Journal survey released Monday has Clinton at 50% support to Sanders' 48% -- down from Clinton's nine-point advantage in the same poll one month ago.

Since more than half of all Democratic voters have already taken part in their states' contests, the national numbers are a limited gauge of where the race stands.

New York is set to hold a key primary on Tuesday, and Clinton is favored by a larger margin there, giving her an opportunity to build her lead among both delegates and in the popular vote.

A Sanders win in New York, though, could shift the tide of the race before five East Coast states vote the following week.

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