Neither Governor Newsom nor First Lady Michelle Obama will become the Democrats’ 2024 presidential candidate. No amount of President Biden’s mental decline, forgetfulness, mumbling, or stumbling can change that. If Mr. Biden can fog up a mirror come Election Day, he will be the nominee. If he cannot, Vice President Harris awaits, on deck, bat in hand.

As for both Mr. Newsom and Mrs. Obama, they would first have to push Ms. Harris aside. For her part, she recently said, “I am ready to serve. There’s no question about that.” That does not sound like someone about to walk the plank. She wants to be president, ran for the job in 2020, and probably expected Mr. Biden, at some point after defeating President Trump, to hand her the baton before November 2024.

With her name on the ballot, Ms. Harris has never lost an election, winning her races for San Francisco district attorney, California attorney general, United States Senate, and vice president. She does not believe she’s disqualified because of her so-called cackle. Nor does she consider herself having failed to determine the “root cause” of the three-year massive influx of illegal immigration when all but the hosts on MSNBC know the root cause is Mr. Biden’s reversal of Mr. Trump’s border policies.

In her identity party, she checks two boxes as a female who identifies as Black. Blacks are the most loyal part of the Democratic base, with Black women more loyal than the men. In a September 2023 article about its CBS News/YouGov poll, CBS News wrote, “Black Democrats are the most enthusiastic about Harris today, as they were three years ago.”

In 2020, Democrats panicked the after the unelectable, self-described “Democrat socialist” Senator Sanders won the Nevada caucuses, briefly becoming the party’s frontrunner. So, Representative James Clyburn, right before the primary in his state, endorsed Mr. Biden and salvaged his meandering campaign. In exchange for Mr. Clyburn’s endorsement, Mr. Biden agreed, if elected, to make his first Supreme Court nominee a Black female.

When it seemed likely that Senator Feinstein would not complete her term, Mr. Newsom announced her replacement would be a Black female. When Feinstein died, Mr. Newsom delivered. Democrats, as a reward for Black loyalty, agreed to move the first 2024 primary to South Carolina, where nearly 30 percent of the voters are Black, giving this voting bloc a greater say in the nomination process.

Mr. Newsom has another problem. Most Americans believe the country is on the wrong track, citing the economy, inflation, gas prices, crime, and illegal immigration. What has Mr. Newsom said or done that would make any of this better?

As I explain in my latest book, “As Goes California: My Mission to Rescue the Golden State,” Mr. Newsom unabashedly resides on the fringe Left of his party. He supported the soft-on-crime district attorneys at San Francisco and Los Angeles. He supports cashless bail. He endorsed Proposition 47, which not only converted theft of nearly $1,000 into a misdemeanor but also took away the ability of cops to force addicts using drugs on the street to either go to rehab or go to jail.

As to Mr. Biden’s ill-advised inflation-inducing spending, Mr. Newsom wants to spend more. As to the Biden war on oil and gas and his anti-drilling policies, Mr. Newsom is an even more ferocious “climate change” warrior, having decreed an end to the sale of new gas-powered vehicles in California by 2035. Even Mr. Biden, who calls climate change “an existential threat,” has not gone that far.

Mr. Newsom expanded the number of illegal aliens in California eligible for taxpayer-provided health care and brags about California’s status as a sanctuary state. Shortly after Mr. Biden’s broadly condemned abrupt pullout from Afghanistan, Mr. Newsom said, “I’m incredibly proud of President Biden.”

This brings us to Mrs. Obama. For the reasons outlined above, Black voters — particularly Black female voters — would resent a ploy to cast Ms. Harris aside, but there is one caveat: The substitute would have to be a popular Black female. Only two fit the bill: Oprah Winfrey and Mrs. Obama. Ms. Winfrey does not want the gig and, despite the hopeful speculation, neither does Mrs. Obama. She hates politics.

So, Ms. Harris it is.