The first lady addressed hundreds of supporters at the National Constitution Center in Philadelphia, hours after holding a fundraising event at The Pierre hotel in New York City.
In Philadelphia, she urged supporters to keep knocking on doors, making phone calls and telling others about the successes of the past four years - ticking off items such as tax cuts, job gains and the president's health care act.
"That's how we did it four years ago. That's how we're going to do it again today," she said of the importance of grass-roots efforts. "Don't forget, this election will be closer than ever before."
President Barack Obama handily won Pennsylvania in 2008 against Republican John McCain, and the state has supported Democrats in the most recent five presidential elections. This year, Republican candidate Mitt Romney is pushing to take the state away from Obama.
The first lady thanked all of the supporters for their hard work, but said there was much more to be done.
"From now until November, Barack needs all of you," she told screaming supporters in Philadelphia. "We still have a long way to go."
Her voice cracking at times, Obama touted her husband's efforts to bail out the auto industry, expand health insurance to more people, reduce the cost of prescription drugs and try to make it so more people can afford to go to college.
She also urged supporters to tell others that the president supports the DREAM Act, saying "He believes it is time to stop denying citizenship to young people just because they are the children of undocumented immigrants."
When recruiting voters, Obama said, supporters should remember that every vote counts.
"In the end, this could all come down to these last few thousand people that we register to vote," she said.
The stop came after a fundraiser in New York City, where Obama made similar pleas. It marked her first visit to Pennsylvania since April, when she spoke at the 911th Air Wing base outside Pittsburgh to recognize veterans and military families.
Pennsylvania has long been a key battleground state in presidential elections, but the state has supported Democrats in the most recent five. Barack Obama handily won Pennsylvania in 2008.
