DUBUQUE, Iowa — As 1,800 mad-as-hell supporters jumped out of their seats and pumped their fists last Sunday, Senator Bernie Sanders of Vermont delivered the message they had come to hear.

We will “give these guys an offer they can’t refuse,” he shouted in the jam-packed gym, vowing to bust up the banks, bring down the billionaire class and smash the political establishment.

“So I welcome you all,” he said, “to the political revolution of 2015.”

The presidential election is, of course, in 2016, but Mr. Sanders can be forgiven for living in the moment. By overtaking Hillary Rodham Clinton in New Hampshire in some polls and drawing tens of thousands of people to his events on the West Coast, as well as thousands in Iowa and Nevada, Mr. Sanders, 73, has recaptured the enthusiasm that fueled the 2008 Obama campaign, with T-shirts that say “Feel the Bern” and show an image of floppy white hair and glasses replacing the famous image in the Obama “Hope” poster by Shepard Fairey.

Unlike that of Mr. Obama, Mr. Sanders’s appeal is less about oratorical lift and finding common ground than about the opportunity his campaign gives disaffected Democrats to vent their anger at the list of national ills they believe are caused by big business and its conservative allies and have been left unaddressed by President Obama. If Mrs. Clinton’s pitch to voters is that she can make the system more effective, Mr. Sanders is arguing that Mr. Obama was naïve to even bother with a system that needs to be fundamentally changed.