The campaign boasted last June, when Mrs. Clinton held her kickoff event on Roosevelt Island in New York, that it had at least one paid staff member in all 50 states. But the effort did not last, and the staff members were soon let go or reassigned. (Mrs. Clinton’s campaign manager, Robby Mook, said they had been hired as temporary workers to sign up volunteers at the start of the campaign, an effort he said had paid off organizationally.)

The focus on Iowa, which still haunts Mrs. Clinton after the stinging upset by Barack Obama there in 2008, has been so intense that even organizers in New Hampshire, which holds its primary on Feb. 9, have complained to the campaign’s leadership that they feel neglected.

On a call with supporters last week, Mrs. Clinton’s aides laid out a scenario in which the race against Mr. Sanders stretched through April, a prospect that they said would require about $50 million for a national ground operation and other expenses.

“It’s not just a question of the first two states or the first four states,” Mr. Mook said in an interview at Sunday’s Democratic debate in Charleston, S.C. “We’re going to keep going into the map as long as it takes.”