President Obama’s remarkable interview last week with the New York Times’s Andrew Ross Sorkin shows why historians are likely to assign Mr. Obama a share of responsibility for the rise of Donald Trump.

To be sure, the president was dealt a tough hand in 2009, and he played it brilliantly at first. His much-criticized Treasury secretary, Timothy Geithner, did what was necessary to pull the U.S. financial system back from the brink. Under intense pressure, the president’s team crafted a package of steps that saved the American...