Bernie Sanders is planning a “major speech” on democratic socialism, the political and economic ideology he embraces in his campaign for the 2016 Democratic presidential nomination.

Sanders told The Associated Press he wants to do it “fairly soon” but hasn’t picked a date. In the Democratic debate last week, rival Hillary Rodham Clinton suggested the Vermont senator would scale back the principles of capitalism and asserted, “We would be making a grave mistake to turn our backs on what built the greatest middle class in history.”

Sanders often speaks about the expansive social programs of some European democracies and economic systems that check the wealth of the richest people as a model for the U.S. He talked about Denmark during the debate, and his campaign is centered on calls for billions more in social spending and higher taxes on the rich.

“We’re going to give a major speech on it,” he said after speaking to more than 200 people at William Penn University in Oskaloosa, Iowa.

Sanders proposes extending publicly financed education beyond high school, to let students go to public colleges and universities tuition-free. “Now is the time,” he said, “because I think the world has changed.”

Though national polls find that Sanders is still trailing Clinton, a globally known former secretary of state, his standing has grown since the summer.

“At the time, people thought I was a fringe candidate,” he told reporters, harking back to his campaign’s start. “We’ve made a lot of progress in the last five months.”