She was there when he hosted Democratic governors at the White House, and she was on the line when he called Israel’s prime minister, and she was at his side on the balcony overlooking the South Lawn when he celebrated the Fourth of July. As the fireworks were about to start, he grabbed her hand and thrust it into the air in a gesture of unity.

In these days of uncertainty at the White House, Vice President Kamala Harris is sticking close to President Biden physically and politically, determined not to let anyone say that she has been anything other than completely loyal. But as a result, it means that the person who may have to step up if he steps down cannot be seen doing anything to prepare for the challenge of a lifetime.

With Mr. Biden’s future on the line, perhaps no one is in a more delicate position than Ms. Harris. For the first time since she took the oath as vice president in January 2021, Democrats are giving her a serious second look, with many coming around to the idea that she could potentially lead the party in November. As a practical matter, though, she has to ignore the chatter and disclaim any interest unless Mr. Biden reverses course and passes her the baton.

“She’s in an awkward position,” said the Rev. Al Sharpton, the civil rights leader, who spoke with Ms. Harris on Friday night at the Essence Festival of Culture in New Orleans. “But the job of vice president is awkward.”

Ms. Harris’s advisers adamantly maintain that she is doing nothing to get ready in case she suddenly has to kick off a campaign for president from a standing start, and there is no known evidence to the contrary. But Democrats acting with her interest at heart, even if not with her permission, are quietly gaming out what a Harris campaign might look like.