SEN. BERNIE Sanders (I-Vt.) is leading in New Hampshire and within striking distance in Iowa, in large part because he is playing the role of uncorrupted anti-establishment crusader. But Mr. Sanders is not a brave truth-teller. He is a politician selling his own brand of fiction to a slice of the country that eagerly wants to buy it.

[Katrina vanden Heuvel: Bernie Sanders is the realist we should elect]

Mr. Sanders’s tale starts with the bad guys: Wall Street and corporate money. The existence of large banks and lax campaign finance laws explains why working Americans are not thriving, he says, and why the progressive agenda has not advanced. Here is a reality check: Wall Street has already undergone a round of reform, significantly reducing the risks big banks pose to the financial system. The evolution and structure of the world economy, not mere corporate deck-stacking, explained many of the big economic challenges the country still faces. And even with radical campaign finance reform, many Americans and their representatives would still oppose the Sanders agenda.

Sen. Bernie Sanders (I-Vt.), spoke about climate change, the Islamic State, racism and his vision for the country at Georgetown University on Nov. 19. Here are the key moments. (Sarah Parnass/The Washington Post)

Mr. Sanders’s story continues with fantastical claims about how he would make the European social model work in the United States. He admits that he would have to raise taxes on the middle class in order to pay for his universal, Medicare-for-all health-care plan, and he promises massive savings on health-care costs that would translate into generous benefits for ordinary people, putting them well ahead, on net. But he does not adequately explain where those massive savings would come from. Getting rid of corporate advertising and overhead would only yield so much. Savings would also have to come from slashing payments to doctors and hospitals and denying benefits that people want.

He would be a braver truth-teller if he explained how he would go about rationing health care like European countries do. His program would be more grounded in reality if he addressed the fact of chronic slow growth in Europe and explained how he would update the 20th-century model of social democracy to accomplish its goals more efficiently. Instead, he promises large benefits and few drawbacks.

[Why Democrats would be insane to nominate Bernie Sanders]

Meanwhile, when asked how Mr. Sanders would tackle future deficits, as he would already be raising taxes for health-care expansion and the rest of his program, his advisers claimed that more government spending “will result in higher growth, which will improve our fiscal situation.” This resembles Republican arguments that tax cuts will juice the economy and pay for themselves — and is equally fanciful.

Mr. Sanders tops off his narrative with a deus ex machina: He assures Democrats concerned about the political obstacles in the way of his agenda that he will lead a “political revolution” that will help him clear the capital of corruption and influence-peddling. This self-regarding analysis implies a national consensus favoring his agenda when there is none and ignores the many legitimate checks and balances in the political system that he cannot wish away.

Mr. Sanders is a lot like many other politicians. Strong ideological preferences guide his thinking, except when politics does, as it has on gun control. When reality is ideologically or politically inconvenient, he and his campaign talk around it. Mr. Sanders’s success so far does not show that the country is ready for a political revolution. It merely proves that many progressives like being told everything they want to hear.