CORALVILLE, Iowa — Bernie Sanders on Saturday unleashed his most forceful rebuke yet of Michael R. Bloomberg’s potential presidential bid, warning the former mayor of New York that he would not be able to “buy this election” and chastising his plan to skip campaigning in the early states.

Speaking at a rally in Coralville, near the liberal home of the University of Iowa, Mr. Sanders, the senator from Vermont, repeatedly addressed Mr. Bloomberg by name, almost daring him to enter a Democratic primary race that has already been in progress for months.

“Our campaign is going to end the grotesque level of income and wealth inequality which exists in America today,” said Mr. Sanders, who was joined by Representative Alexandria Ocasio-Cortez, a standard-bearer of the progressive left. “So tonight we say to Michael Bloomberg and other billionaires: Sorry, you ain’t going to buy this election.”

He also derided Mr. Bloomberg’s intended strategy of bypassing the key early voting states where so many of the current candidates are devoting time, money and resources.