President Biden forcefully says he isn’t withdrawing from the presidential race. But if he does, there’s a reason or two that many leaders of his party think the next nominee would be Vice President Kamala Harris.

There’s the built-in Democratic base. There’s the easier logistics. There’s the history to be made.

And yes, there’s the money.

If Democrats carried out a stunning switch at the top of their ticket, what happens next would have no modern precedent — including in the campaign finance realm. But we do know a few things:

Kamala Harris would have a $91 million (or so) edge.

Over the last two years, Mr. Biden and Ms. Harris have together raised hundreds of millions of dollars for their re-election bid. That money has been split across the Biden campaign, the Democratic National Committee, almost every state Democratic Party, and various joint-fund-raising committees that cycle cash among all of those entities.

As of June 30, all of those groups had about $240 million in cash on hand. Most of that money — say, the stockpile at the Democratic National Committee — wouldn’t be affected by a change of nominee.

But the most important money is in the accounts held by the Biden-Harris campaign committee: $91 million as of May 30. (The campaign hasn’t disclosed how much it had as of June 30.) That money has been raised by the Biden-Harris ticket, and belongs to the Biden-Harris ticket. The only people whom that money follows are, you guessed it, Mr. Biden and Ms. Harris.

So if Mr. Biden were to cede his role and Ms. Harris were to be officially nominated (with a new No. 2), her new ticket would have almost no interruption financially. She would have immediate access to the $91 million or so in cash on hand, an important consideration given how former President Donald J. Trump and Republicans have rapidly caught up to the Democrats in fund-raising.