The poll, from Quinnipiac University, found Clinton leading Sanders among national Democratic-primary voters, 44 percent to 42 percent.
That was a wild swing from a mid-December Quinnipiac poll that found Clinton leading 61 percent to 30 percent nationally over Sanders.
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"Democrats nationwide are feeling the Bern as Sen. Bernie Sanders closes a 31-point gap to tie Secretary Hillary Clinton," said Tim Malloy, the assistant director of the Quinnipiac poll.
The Quinnipiac survey is the most bullish for Sanders on a national scale recently. Clinton remained ahead of Sanders in a Real Clear Politics average of recent national surveys by about 13 points.
Still, the Friday survey presented fresh signs of momentum for Sanders, who surprised much of the political world when he came close to overtaking Clinton in the Monday-night Iowa caucuses. He also appears primed for a win in New Hampshire, which holds its primaries next Tuesday: He's up by more than 20 points in an average of recent polls.
The Quinnipiac poll found that Sanders would fare better than Clinton in hypothetical general-election matchups, an argument he has started to make on the campaign trail. For example, while Clinton would lose to Sen. Marco Rubio (R-Florida) by seven points, Sanders would tie him, according to the survey. He would also double Clinton's margin of victory over real-estate magnate Donald Trump.
For his part, Trump continued to lead on the Republican side, according to Quinnipiac. He received 31 percent of the vote, followed by Sen. Ted Cruz (R-Texas) at 22% and Rubio at 19%.
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