Four leading Democratic economists sharply criticized Sen. Bernie Sanders for citing “extreme claims” about the economic effects of his campaign proposals, the latest in a stream of critiques from Democrats over details of his platform.

Criticism has also been directed at Mr. Sanders’s plan for a single-payer, government-run health-care plan, with critics saying he underestimates the costs of providing health care to all Americans and overestimates the revenue his plan would generate.

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