After meeting with Israel’s prime minister this week, Vice President Kamala Harris said she “will not be silent.” She was referring to her concerns about Palestinian suffering in the Gaza war, but in a way it was a larger declaration of independence.

For nearly four years, she has been the quiet understudy, relegated to the role of the supportive deputy while President Biden made pronouncements. Now she has suddenly been thrust to the fore as the new presumptive Democratic presidential nominee, and neither silence nor agreeable head nods are sufficient any more.

The challenge for her over the next 100 days will be to find her own voice without overtly breaking with Mr. Biden, a delicate political high-wire act without a reliable net. Every statement she makes, every sentence she utters, will be scrutinized to determine whether it is consistent with the president she serves. Yet even as she wants to demonstrate loyalty to Mr. Biden, she also hopes to show the public who she is.

She is fortunate in that she and Mr. Biden do not diverge all that much, according to people who have worked with them. While friction between presidents and their vice presidents is common, there have been few notable instances where Mr. Biden and Ms. Harris have been reported to be at odds. So for her, it may not be as difficult to suppress contrary instincts in the truncated election campaign she faces as it has been for other vice presidents eager to differentiate themselves.

But this is a balancing act being figured out on the fly. Because Mr. Biden was running himself until less than a week ago, neither he nor Ms. Harris has had much time to figure out how to coordinate their messages. It was notable that Mr. Biden left it to Ms. Harris on Thursday to be the public voice of the administration during the White House visit by Prime Minister Benjamin Netanyahu of Israel, taking the silent role himself.

Mr. Biden cares deeply about keeping former President Donald J. Trump out of the White House and therefore has reason to be invested in Ms. Harris’s success. He also knows that because, until he was forced to quit the race, he had insisted on running again despite concerns about his age, many will blame him for not ceding the stage earlier if Mr. Trump wins.