Sen. Bernie Sanders (I-Vt.) is narrowly leading a tight cluster of four top candidates in Iowa three weeks before the Feb. 3 caucuses there, according to a new poll released Friday evening by the Des Moines Register and CNN.

The survey is the first to have Sanders leading in the state, and it shows that he enjoys support from 20 percent of likely voters. Sen. Elizabeth Warren (D-Mass.) took 17 percent support, former South Bend, Ind., mayor Pete Buttigieg had 16 percent, and former vice president Joe Biden came in with 15 percent.

No other candidate reached double digits.

The survey of about 700 likely Iowa caucus-goers had a margin of error of 3.7 percent, putting the group in a near four-way tie for first place — a highly unusual split so close to the first votes of the primary season.

Still, the poll showed that some dynamics in the race have subtly changed since the same group surveyed voters in mid-November.

Most notably, Buttigieg, who had surged into first place in the last Des Moines Register-CNN poll, dropped nine percentage points and is now essentially in third place. And Sanders increased his standing by five percentage points, going to 20 percent from 15 percent in November.

Warren and Biden saw little change in their standings, with Warren picking up one percentage point and Biden remaining even.