First Lady Michelle Obama speaks at LaSalle University in Philadelphia, Wednesday, Sept. 28, 2016, as she campaigns for presidential candidate Hillary Clinton.

"Experience matters. Preparation matters. Temperament matters. Hillary Clinton has it all. She's the real deal," Obama told a rally at La Salle University in Philadelphia.

Referring to Trump only as Clinton's "opponent," the first lady slammed the billionaire developer for his "erratic" behavior and years of questions about her husband's birthplace. She described Clinton as "steady and measured" and urged young people to vote for the former secretary of state even though she may not be "the perfect candidate."

Michelle Obama on Wednesday attacked Donald Trump 's character without mentioning his name and touted Hillary Clinton 's tenacity in a pitch to young voters in swing-state Pennsylvania.

The Clinton campaign has attempted to mobilize young voters in swing states with the help of popular surrogates like Michelle Obama and Sen. Bernie Sanders, who mounted a populist Democratic primary challenge to Clinton. Clinton has enjoyed less support than President Barack Obama did with young voters, who are a key demographic for Democrats as Republicans typically carry older voters.

Some young voters, dissatisfied with Clinton's perceived "insider" reputation or concerned about the Democratic National Committee's ethics, have signaled they will vote for a third-party candidate or stay home altogether. Clinton has a 1.8-point lead in an average of recent Pennsylvania polls, down from 10 near the end of August, and the Green Party's Jill Stein has drawn about 2.6 percent of support on average, according to RealClearPolitics.

"If you vote for someone other than Hillary or don't vote at all, you are helping to elect Hillary's opponent. And the stakes of taking that chance are too high," the first lady said.

Mrs. Obama touted Clinton to young voters by describing work she has done to improve education and expand health care and child care as both a private and public figure.

She also attacked Trump's off-the-cuff style and temperament, pointing in particular to comments he made at the first presidential debate on Monday. She said that Trump's assertions that not paying taxes makes you "smart" or that taking advantage of the mortgage crisis is "good business" show he is not prepared to become president.

"The presidency doesn't change who you are, it reveals who you are," she said. "And the same is true of a presidential campaign."

Mrs. Obama said Trump's effort to get her husband to release his birth certificate, which many saw as an attempt to delegitimize the first African-American president, cannot be swept under the rug "by an insincere sentence uttered at a press conference."

Mrs. Obama will campaign for Clinton later Wednesday in Pittsburgh, another urban center that will be crucial for the Democrats in Pennsylvania.