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WASHINGTON — With the Democratic nomination race now down to a one-on-one contest between former Vice President Joe Biden and Sen. Bernie Sanders of Vermont, Democratic primary voters now back Biden — who was a distant second to Sanders just one month ago — by an overwhelming 2-to-1 ratio, according to a new NBC News/Wall Street Journal poll.

The survey found that 61 percent of Democratic voters support Biden, while just 32 percent back Sanders. Four percent choose Rep. Tulsi Gabbard of Hawaii, who has not yet dropped out of the race despite failing to finish in the top three in any state primary or caucus.

Biden's surge of more than 45 percentage points in four weeks shows how quickly he became the consensus choice of Democratic voters as the field narrowed to just two major candidates. The NBC News/WSJ poll in February, which was conducted before Biden's decisive win in the South Carolina primary changed the trajectory of the race, found Sanders besting Biden, 27 percent to 15 percent, while candidates who have since dropped out — former New York Mayor Michael Bloomberg, Sen. Elizabeth Warren of Massachusetts, former South Bend, Indiana, Mayor Pete Buttigieg and Sen. Amy Klobuchar of Minnesota — divided the rest of the vote.

All of those candidates except Warren have since thrown their support behind Biden.

Democratic voters are also significantly more likely than they were last month to say they are enthusiastic about Biden's campaign. In February, just 13 percent said they were enthusiastic about him, while 43 percent said they were merely comfortable, and a combined 43 percent said they had reservations or were uncomfortable. Now, 37 percent say they're enthusiastic about Biden, 37 percent say they are comfortable, and just 25 percent express reservations or discomfort.

For Sanders, less has changed since February. This month, a combined 66 percent of Democratic voters say they are either enthusiastic (27 percent) or comfortable (39 percent) with him. Last month, it was a combined 65 percent.

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The former vice president has significant leads among almost every key Democratic voting group; he has the support of 60 percent of white voters, 77 percent of African-American voters, 64 percent of women and 79 percent of voters over 50.

But, as Sanders noted Wednesday when he announced his intention to stay in the race, Biden's performance with young Democratic voters remains a glaring weak spot. Among voters under 35, just a quarter chose Biden, while 7-in-10 pick Sanders.

Biden leads Trump by 9 points in a one-to-one matchup

Among all registered voters, Biden leads President Donald Trump outside the poll's margin of error in a head-to-head contest. In a hypothetical one-on-one general election contest, 52 percent of all voters say they would choose Biden, while 43 percent say they would choose Trump.

For Sanders, it's 49 percent saying they would support him, while 45 percent back Trump.

In the matchup between Biden and Trump, Biden has the backing of a majority of independents (59 percent), women (63 percent) and white voters with college degrees (53 percent). He is also the overwhelming choice of nonwhite voters, getting support from 70 percent of Latinos and 84 percent of black voters.

Trump receives majority support from white voters (51 percent), men (53 percent) and white voters without college degrees (57 percent).

Among suburban voters, Biden gets 49 percent, while Trump gets 45 percent.

And among voters in 2016 swing states, Biden gets 50 percent, while Trump gets 42 percent.

Still, Trump continues to enjoy the most fervent support from his backers. Among all voters, 27 percent say they're enthusiastic about his candidacy, compared with 15 percent for Biden and 13 percent for Sanders.

But nearly half of all voters — 48 percent — say they're very uncomfortable with his run. That's compared with 31 percent who say the same of Biden and 42 percent who say the same of Sanders.

The NBC News/WSJ live-caller poll was conducted March 11-13, 2020. The poll surveyed 900 registered voters, including 438 Democratic primary voters. The margin of error for all voters is +/- 3.27 percentage points. The margin of error for Democratic primary voters is +/- 4.68 percentage points.