LAS VEGAS — For much of the presidential election of 2008, Barack Obama’s campaign was Emma Guerrero’s life. She was one of a dozen volunteers who showed up at an Obama campaign office here every night, taking time from her studies at the University of Nevada, Las Vegas, to be part of what she still remembers as the most exciting period of her life.

It was largely because of Ms. Guerrero — and hundreds of other college students like her across the country — that Mr. Obama assembled a formidable machine that helped him roll to victory in 2008, a triumph that included putting Nevada into the Democratic column for the first time in 12 years.

“We did everything,” she said. “We went canvassing. Phone banking. Cleaning the offices. Taking out my bosses’ dry cleaning. Whatever they needed. It was such an amazing time because we all believed and wanted him to get elected.”

Ms. Guerrero said that she did not blame Mr. Obama for the 13.4 percent unemployment rate that has gripped this state, and that she was still likely to vote for him. But as she looks to graduation this June and her job hunt ahead, the emotion she feels is fear, and she cannot imagine having the time or spirit to work for Mr. Obama.