We face grave challenges—China, Russia, the endurance of the American economy. Who leads us matters. Ms. Harris should set her mind primarily on the deep and profound responsibilities of the job she may have to fill. She should do this as an act of will. Only secondarily should she be thinking about her political prospects.

She seems to have the order confused. And when that is true everybody can tell.

Second, she must make herself useful. She’s there to help the president. Recent vice presidents who were good at their job and evaded this kind of criticism were longtime Washington hands who made their experience useful to the president, helping him navigate the town, find old levers, forge new relationships. George H.W. Bush did this for Californian Ronald Reagan ; Al Gore knew things that benefited Bill Clinton, former governor of Arkansas.

The Washington insider path is closed to Ms. Harris because she’s relatively new to town and her president’s experience dwarfs hers.

But here’s something she could do for Mr. Biden to be useful to his larger project. She could lend what skills she has to the public presentation of the administration’s stands.