As the Republican candidates prepared to debate in Colorado, the land of legal marijuana, Senator Bernie Sanders of Vermont told an audience of college students in Virginia that “in my view, the time is long overdue for us to remove the federal prohibition on marijuana.”

At the event at George Mason University, which was live-streamed to about 300 college campuses around the country, Mr. Sanders spoke in ominous tones about climate change, a rigged economic system and a broken criminal justice system. But as the live stream “stopped streaming,” as Mr. Sanders’s website put it, he focused on an issue that was a crowd-pleaser to the young audience.

Mr. Sanders, who often gets big cheers on the campaign trail when he calls for the decriminalization of marijuana, said that states should have the right to regulate marijuana the same way that state and local laws now govern sales of alcohol and tobacco.

“That means,” he said, “that recognized businesses in states that have legalized marijuana should be fully able to use the banking system without fear of federal prosecution.”