“Everything I’m telling you may end up being wrong,” Bernie Sanders, the Vermont senator seeking the Democratic nomination for president, said early in our conversation on Thursday.

I had written an article concluding he had slim chances of winning the nomination, based on the limits of his ideological appeal. Mr. Sanders was building a coalition of liberals, as have past liberal anti-establishment Democrats, and it was likely to fall short.

But Mr. Sanders, who has surged in the polls against Hillary Clinton, called to advance a different theory of the race. “I look at these things more from a class perspective,” he said.

“I’m not a liberal. Never have been. I’m a progressive who mostly focuses on the working and middle class.”