In nominating Joe Biden, Democrats aren’t choosing a “moderate.” They’re choosing liberalism over revolution. “Joe and I have a very different voting record,” Bernie Sanders said after Super Tuesday. That is demonstrably true. Their records differ in substantial ways. He went on: “Joe and I have a very different vision for the future of this country.” That is not quite right. The idea that Mr. Biden has a “vision for the future” is preposterous. He has a vision for the past, and even that is cloudy.

I don’t criticize him for it. I am a conservative. “Vision,” in my understanding, is for prophets, not statesmen. But Mr. Biden is no conservative. He is a liberal, and liberalism needs vision.

Mr. Sanders is a radical, not a liberal. The liberal worldview seeks a more equitable and open polity by means of piecemeal political reform. The radical outlook envisions a new world, not an incrementally better one. He wants to remake the U.S. economy and banish all forms of inequality.

With Mr. Biden’s ascension and Mr. Sanders’s decision this week to suspend his campaign, Democrats are again choosing liberalism. The important thing to understand about modern American liberalism, though, is that it is a spent force. It is out of ideas. It is visionary, but it no longer sees much of anything. That Mr. Biden has been reduced to protesting the Trump administration’s handling of the coronavirus outbreak, safely tucked away in his basement, nicely symbolizes liberalism’s impotence.

The liberal politician can offer a collection of ideas, but those ideas are old ones repackaged. He can offer a vision, but it is the same vision liberal politicians were offering 20 or 40 years ago. Accepting the 1992 Democratic presidential nomination, Bill Clinton ridiculed President George H.W. Bush’s disdain for “the vision thing.” Mr. Clinton quoted Proverbs 29:18: “Where there is no vision, the people perish.” The goals he enunciated in that speech were more or less the same goals every other Democratic nominee has endorsed since the middle of the 20th century: a fair shot for working Americans, new investments in schools, expansion of access to health care. Mr. Biden could give that speech today and few would suspect him of plagiarism.