Mr. Obama engendered such passion last year that his allies believed they were on the verge of creating a movement that could be mobilized again. But if a week’s worth of events are any measure here in Iowa, it may not be so easy to reignite the machine that overwhelmed Republicans a year ago.

More than a dozen campaign volunteers, precinct captains and team leaders from all corners of Iowa, who dedicated a large share of their time in 2007 and 2008 to Mr. Obama, said in interviews this week that they supported the president completely but were taking a break from politics and were not active members of Organizing for America.

Some said they were reluctant to talk to their neighbors about something personal and complicated like health care. And others expressed frustration at the genteel approach, asking why Democrats were not filling the town-hall-style meetings of Senator Charles E. Grassley of Iowa, the ranking Republican on the Finance Committee negotiating health care legislation, or Representative Leonard L. Boswell, a member of the moderate Blue Dog Democratic group…

But even among those who turned out for the meetings, many of whom had Obama buttons affixed to their shirts and spoke glowingly of the president, there was a sense of fatigue at the prospect of returning to the political calisthenics the Obama army once required.