www.nytimes.com/…

A survey from Quinnipiac University found that 49 percent of likely Democratic caucusgoers supported Mr. Sanders and 45 percent backed Mrs. Clinton. The poll had a margin of error of plus or minus four percentage points.

Trailing the two leading candidates in Iowa is Martin O’Malley, the former Maryland governor, with 4 percent support. With the race so close, Mr. O’Malley’s backers could sway the outcome on caucus night.