Biden is struggling in Iowa and his supporters there know why

Yet voters at Mr. Biden’s events, along with county chairs and party strategists, characterize his on-the-ground organization as scattershot, visibly present in some counties but barely detectable in others. His events are often relatively small and sometimes subdued affairs, and in a state where enthusiasm can make or break a candidate on caucus night — a big part of caucusing centers on persuading friends and neighbors — Mr. Biden’s operation has found it difficult to build contagious excitement, these Democrats say.

There is also the sense among many Iowa Democrats that Mr. Biden, who entered the race later than many of his rivals, has been less engaged in the state than his top rivals. He has made roughly 50 stops in Iowa since joining the race in April, according to the Des Moines Register’s candidate tracker, far fewer than many of his opponents.

“This is prime political season in Iowa and most candidates are spending a good deal of time visiting Iowa,” said Joey Norris, the Democratic chair in Montgomery County, Iowa, where Mr. Buttigieg plans to campaign on Monday. “The Biden campaign has been notably absent.”