Vermont Sen. Bernie Sanders surged to the lead in a closely watched poll of Iowa voters, according to results released Friday.

Twenty percent of likely Democratic caucusgoers chose Sanders as their first pick for president in the Des Moines Register-CNN-Mediacom poll ahead of Iowa’s statewide caucuses on Feb. 3. That’s a five point increase for Sanders since the same poll was conducted in November.

Massachusetts Sen. Elizabeth Warren (17%), former South Bend, Indiana, Mayor Pete Buttigieg (16%) and former Vice President Joe Biden (15%) rounded out the top four Democrats in the latest survey.

Buttigieg, who led the November poll, lost nine points. Warren gained 1 percentage point, while Biden stayed even.

The poll, conducted from Jan. 2-8, is based on telephone interviews with 3,131 registered Iowa voters, including 701 who said they are likely to attend the 2020 Democratic caucuses. The poll of likely Democratic caucusgoers has a margin of error of plus or minus 3.7%.

???????????? NEW #IOWAPOLL ????????????

Sanders: 20% (+5)
Warren: 17% (+1)
Buttigieg: 16% (-9)
Biden: 15% (-)
Klobuchar: 6% (-)
Yang: 5% (+2)
Booker: 3% (-)
Steyer: 2% (-1)
Gabbard: 2% (-1)
Bloomberg: 1% (-1)
Not sure: 11% (+6)

No other candidate polled above 0%. https://t.co/zI54dRncgk

— Des Moines Register (@DMRegister) January 10, 2020

Sanders has surged of late despite suffering a heart attack in early October. Warren captured some of Sanders’s supporters after his illness, but her momentum has faded amid scrutiny of her Medicare for All plan.

Biden came in fourth in the latest poll; however, he holds a commanding lead in national polls. Biden is averaging 29% in recent polls, according to RealClearPolitics. Sanders is polling just above 20%, on average, while Warren is just shy of 15%.