With Hillary Clinton's lead in the polls over Donald Trump all but gone, her campaign is pushing prominent Democrats, including former primary rival Bernie Sanders, into the field in an effort to lock up the youth vote for the Democratic nominee.

The effort began in earnest Friday, when first lady Michelle Obama addressed a rally at George Mason University in northern Virginia. She warned young voters against being "tired or turned off," and urged them to rally around Clinton, "particularly given the alternative."

Despite the first lady's efforts, the Wall Street Journal reported some members of the crowd could be heard chanting "Four more years!"

Clinton led most national polls by double digits in the days following the Democratic convention, but most recent polls have the race in a statistical dead heat. Much of that can be attributed to a drop in her support among young people.

In a Fox News poll taken in early August, days after the convention, Clinton led Trump by 27 points among voters under 35. In the most recent Fox News poll, Clinton led Trump by just five points among likely voters under 35.

Many of the voters who once backed Clinton appear to have thrown their support to Libertarian candidate Gary Johnson. In the recent Fox News poll, Johnson only garnered the support of 8 percent of all likely voters. However, Johnson polled at 16 percent among under-35s.

Sanders, who mounted a surprisingly strong primary challenge to Clinton with the help of overwhelming youth support, was scheduled to speak on Clinton's behalf at two Ohio colleges Saturday. A recent CNN/ORC poll showed Trump with a five-point lead over Clinton in the Buckeye State.

"I can criticize Hillary Clinton for this, that, and the other thing," Sanders told CNN Friday. "Trump literally changes his views every other day."

The self-described democratic socialist went on to call the real estate mogul "a fraud and a phony" who was running a "campaign of bigotry."

Clinton pollster and adviser Joel Benenson admitted to the Journal Friday that the campaign "closed the deal" with young voters. Another Clinton campaign official said they planned to stress a message that a vote for a third-party candidate like Johnson or Jill Stein of the Green Party was in effect a vote for Trump.

But other Clinton supporters believe the best advocate may be Michelle Obama, whom they want in battleground states as much as possible between now and Election Day.

Jennifer Palmieri, Clinton's communications director and a former Obama adviser, called the first lady "an advocate without peer."

"There is no other surrogate with the reach, credibility and respect she has," Palmieri said.

The Associated Press contributed to this report.