CHICAGO (CBS) — U.S. Sen. Bernie Sanders returned to his alma mater on Monday, for his second campaign stop in Chicago since announcing his bid for the Democratic nomination for president in April.

“This is exactly the place where I was graduated from in 1964,” Sanders said at the University of Chicago, where he was speaking as part of the Institute of Politics “Road to 2016” series.

READ MORE: Chicago Weather: Winter Weather Advisories In Effect; Snow Arrives For Monday Morning Commute

Sanders, an independent from Vermont, said it was the Hyde Park campus where he learned about organized labor, and democratic socialism.

“I learned a lot from folks who were involved – and have been involved for decades – in the civil rights movement, in the peace movement. I got a job working for a trade union here in Chicago, which introduced me to the trade union movement. I learned here about democratic socialism,” he said.

READ MORE: 4 Dead, 23 Wounded In Weekend Shootings Across Chicago

He told the standing-room-only audience at Rockefeller Chapel – mostly U of C students – it was up to them to make a difference.

“There is nothing that I am telling you today that is pie in the sky, that is utopian; nothing. We can accomplish all of that and more, but we will not accomplish that if 80 percent of young people do not vote,” he said.

MORE NEWS: Melissa Ortega, 8-Year-Old Girl Killed In Little Village Shooting, Had Just Emigrated From Mexico

Polls have shown Sanders closing a significant gap with Democratic frontrunner Hillary Clinton in the last few months. While Clinton led had a 62 percent to 10 percent lead on Sanders at the start of the year, the most recent polls show Clinton with 42 to 44 percent of the vote, compared to 25 to 35 percent for Sanders.