Her DNC speech was fine, but the race remains a toss-up. It’s all going to come down to policy.

The convention itself was a great success, with some sharp and memorable moments. The convention’s overall impression was summed up by a relative who, watching on the second night, observed: “This is what they’re saying: ‘We’re a grand coalition, we’re more of a vibe than a party, and we’re not him.’ Plenty of people will want to join that.”

There was hunger—“We’ll sleep when we’re dead”—and boldness, too. They stole traditional Republican themes (faith, patriotism) and claimed them as their own. Also impressive was the degree to which they cast a magic conjuring sorcery spell in which viewers got the feeling the whole purpose of the Democratic Party is to break away from a grim and doom-laden reigning regime . . . when they’ve been in charge for 3½ years. Something else. The Democratic Party has more substantial characters of recent American history to parade around on stage. The Clintons, the Obamas, Jesse Jackson...

And now the race. It’s a toss-up, no one knows where this is going. Ms. Harris is limited in this respect: She never had to be anything but a person of the left to rise in the Democratic bastion of California. She never had to talk to a conservative or a Republican. What she had to do to succeed in her Democratic state was juggle different party coalitions.

This week she appeared before some smallish crowds and gatherings, holding a mic, walking along a stage, and speaking publicly in a way that might have been planned but wasn’t scripted. And here you saw her limit as a public figure: Unscripted, she’s word-saying. She isn’t having a thought and looking for the right words to express it, she’s saying words and hoping they’ll amount to a thought.

She’ll have to get over that. She just did a pretty good job of talking to America. Now she’ll have to do it every day.

In any case, her weak points aren’t really what the Trump people think—popping off in arias that go nowhere, fumbling when pressed. Her real weak point is policy. She will be perceived by many voters as farther to the left than they want to go. One of the reasons Democrats had such unity this week is that with Ms. Harris’s elevation, the progressives kind of won a long struggle. The moderate Hillary Clinton was defeated by the seemingly more progressive Barack Obama in 2008. The moderate Joe Biden beat all comers to his left but, in his economic and social policy, tugged progressive because that’s where the rising power in his party was. Ms. Harris is of and from that rising power. We’re going to start hearing the phrase “pragmatic progressive” in the coming months. This is going to be all about policy.

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