WASHINGTON — Bernie Sanders has the slight edge in a tight race in Iowa, according to the state’s most accurate pollster.

Sanders leads the way with 20% support of likely Iowa Democratic caucus-goers in a new poll conducted by the well-respected Ann Selzer for the Des Moines Register and CNN. Sen. Elizabeth Warren is right behind him at 17%, with South Bend Mayor Pete Buttigieg is at 16% and former Vice President Joe Biden is at 15% in the survey.

The poll comes just weeks ahead of Iowa’s Feb. 3 caucuses, the official start of the 2020 campaign and a key moment for candidates as they try to lock down the nomination. And it shows a close four-way contest where all four candidates have a real shot at winning the influential contest.

These are good numbers for Sanders — he’s the only one who’s shown any growth in support since Selzer’s last poll in November. Buttigieg led in that survey with 25%, followed by Warren at 16% and Biden and Sanders at 15% apiece. These latest numbers also aren’t good for Buttigieg, who’s slipped nine points since November in Selzer’s poll.

“There’s no denying that this is a good poll for Bernie Sanders. He leads, but it’s not an uncontested lead,” Selzer told the Des Moines Register. “He’s got a firmer grip on his supporters than the rest of his compatriots.”

But Sanders’ lead is within the poll’s 3.7-point margin of error — he’s statistically tied with the others. With weeks to go, any of the four top-polling candidates could still easily pull out a win.

The Iowa caucuses often dictate which candidates can keep running, knocking out a bevy of lower-polling candidates.

Buttigieg likely has the most riding on the state. The upstart mayor’s support in poll after poll comes from white and college-educated voters, who are overrepresented in Iowa compared to the party as a whole. If he can’t win in Iowa and New Hampshire, it’s hard to see how he’ll capture the nomination.

Iowa’s results could also firm up the pecking order among more progressive candidates. Warren and Sanders have been battling for more liberal voters, and though Warren has appealed to more ideologically mixed group, they both likely need a strong finish in the state as they head into New Hampshire, a state near both their homes that could be make-or-break for either candidate.

Biden can probably afford to lose Iowa and possibly New Hampshire as well — his path to the nomination runs through more diverse states where he’s polling better, including early-voting Nevada and South Carolina. But he has to avoid an embarrassing setback in the state.

New Hampshire’s primary looks just as close. The two reputable polls of the state’s primary released this week — from CBS and Monmouth University — both found margin-of-error races.

Selzer is widely regarded as far and away the most accurate pollster of Iowa, with her numbers taking near-mythic status amongst political gurus. And campaign staff and other Iowa Democrats gurus have been waiting on pins and needles for these numbers. In conversations over the last few days, multiple Iowa Democrats caveated their thoughts on the race with a variation of “unless Selzer shows I’m wrong.”

She’s not perfect. Her last poll of the 2016 caucuses had President Trump leading by five, when Sen. Ted Cruz (R-Texas) went on to win by three. She also got the 2004 election wrong, but her three-decade track record is impressive, including in a number of races where her numbers conflicted with other public polling and were spot on.

That happened in 2008, when she nailed then-candidate Barack Obama’s larger-than-expected margin of victory, and in 2014, when she was the only pollster who came close to Sen. Joni Ernst’s (R-Iowa) comfortable win when others were showing a neck-and-neck race.

Cover image: Democratic presidential candidate Sen. Bernie Sanders (I-VT) speaks at town hall at the National Motorcycle Museum on January 3, 2020 in Anamosa, Iowa. (Photo by Stephen Maturen/Getty Images)