U.S. First Lady Michelle Obama on Wednesday slammed Republican presidential nominee Donald Trump criticizing him for his "erratic and threatening" behavior that would put America at risk.

While addressing an enthusiastic crowd in Philadelphia, Michelle said that candidates don't need change once they become President and that America needs an adult in the White House.

The Republican presidential nominee "traffics in prejudice, fears and lies" and consistently insults women, said Michelle during a rally for Democratic presidential nominee Hillary Clinton in Philadelphia.

Michelle added that it was insincere, among the "hurtful and deceitful" questions raised over her husband birthplace, she said that questions were deliberately designed to undermine the presidency of her husband.

Meanwhile, at a campaign rally for Hillary Clinton at La Salle University, Michelle urged the audience not to vote for third-party candidates Gary Johnson and Jill Stein, explaining that casting "protest votes" would directly help Trump. 

She slammed the idea of there being a "perfect candidate" in the 2016 election, saying no such person exists in any race. This one, she said, features two "very different candidates" who will have an impact on the future of United States.

The first lady took strong exception to Trump's press briefing on Sep. 16, where he finally acknowledged that President Obama was born in the United States. 

Although the Obama campaign released his birth certificate in 2008 and the Honolulu Advertiser reported his birth in a standard newspaper announcement in August 1961, Trump tried to raise doubts.

The Hillary Clinton campaign is eyeing to make use of Obama's connections with young audiences, a role that Michelle has already executed for her husband during 2012 presidential elections.

The recent poll showed 42 percent American voters supported Clinton while 38 percent supported Trump. Over the past few weeks Clinton has maintained a lead of between 4 and 6 points over Trump.

Clinton has mostly led Trump in the poll during the 2016 campaign, though her advantage has narrowed since the end of the Democratic and Republican national conventions in July.