Mark Twain was said to have written: “History does not repeat itself, but it rhymes.”

Today, we look back a half-century to see what precedents exist for how Democratic power brokers just might address the problem of keeping their party in power, without relying on either a mentally challenged president or an intellectually challenged vice president.

Make no mistake about it. There are powerful Democratic forces lurking behind Joe Biden’s throne who even now are plotting ways to shove him to the side. His performance at the Group of Seven conference in Italy, where Italian Prime Minister Giorgia Meloni had to take him by the arm after he wandered off from his colleagues, might have been the final straw.

The problem they face is how to avoid elevating to the presidency the nation’s first female and first nonwhite vice president without losing support from the Democrats’ most reliable constituencies.

With these people, no strategy is off the table in order to retain political power.

Let’s consider one approach that could be hatched in a smoke-filled room in the coming weeks that could turn this fall’s presidential election on its head.

The Rockefeller Precedent

Richard Nixon hand-picked the little-known Maryland Gov. Spiro Agnew as his running mate for his win in 1968. Agnew turned out to be a forerunner of former President Donald Trump, aided by the rhetorical skills of Pat Buchanan, in attacking the press as “nattering nabobs of negativism.”

Despite the flack he took for being Nixon’s hatchet man, Nixon stuck with him again for his landslide victory in 1972 — carrying every state but Massachusetts.

However, in less than a year, Agnew came under investigation by the U.S. attorney for Maryland, pleaded no contest to a single felony charge of tax evasion and resigned from office.

To fill the vice presidency, in October 1973, Nixon appointed House Minority Leader Gerald Ford.

It had been only six years since the states had ratified the 25th Amendment, which provided a new method to fill a vacancy in the vice presidency. Under that Amendment, the president nominates a new vice president who takes office upon confirmation by a majority vote of both Houses of Congress.

There are no restrictions on who the president may nominate — it need not be a person who has ever been in elected or appointed office.

Long a fixture on Capitol Hill, Ford was confirmed easily by both the Senate and the House and sworn in on Dec. 6, 1973.

Facing his own problem with the Watergate scandal, Nixon was forced to resign from the presidency on Aug. 9, 1974, and was succeeded by Ford, for whom no American had ever voted for national office.

Less than two weeks later, President Ford nominated former New York Gov. Nelson Rockefeller as vice president. He too saw swift Senate and House confirmation and was sworn in on Dec. 19, 1974.

At that point, the nation had not only an unelected president but also an unelected vice president. And all those changes had occurred only 25 months after Nixon-Agnew took the election by storm, winning 49 states and over 60 percent of the popular vote.

Does that historical illustration give anyone ideas?

If Past Is Prologue

In the last few weeks, talking heads have suggested that Supreme Court Justice Sonia Sotomayor should step down. She is 69 years old and says she has diabetes, and Democrats could appeal to her to resign so her replacement could be chosen by Biden.

A resignation would avoid the risk of a vacancy occurring during a second Trump administration. (No Democrat wants to repeat the scenario where Ruth Bader Ginsburg hung on until after President Barack Obama left office, resulting in Trump nominating Amy Coney Barrett.)

Just who is there who might be able to fill what is now considered both a “female” and “minority” seat on the high court? Well, a minority female might be a good choice for a Democratic president. And, after every recent Supreme Court decision that does not go Biden’s way, Kamala Harris seems to launch an attack on the justices, indicating she would have done better.

Sounds like the vice president might welcome an appointment where her clerks could write her opinions and she would not be called on to deliver “word salad” speeches.

That moves her out of the way.

At that point, Biden could use that 25th Amendment to appoint someone. Who might that be? Could it be Hillary Clinton? Lots of Democrat politicians would line up for that appointment.

Whomever it may be, after confirmation, that would be a great time for Biden to decide that his health has taken a surprising, sudden downturn and resign.

At that point, all that would be needed is for the new president to pick a new vice president, and we are back to the 1970s.

Someone like California Gov. Gavin Newsom? Presto chango: As the Republicans did in the 1970s, the Democrats could do in the coming weeks, giving us an unelected president and vice president on the general election ballot.

Let’s look back a half-century to see how that worked out for the Republicans.

With President Ford facing a tough nomination challenge from Ronald Reagan, Rockefeller (despised by supporters of Barry Goldwater) offered to step aside, and Ford eventually agreed.

At the 1976 Republican National Convention, the delegates selected Kansas Sen. Bob Dole as Ford’s running mate.

Four years after having trusted Nixon-Agnew and having both candidates disappoint, the voters decided not to trust Ford-Dole. The ticket was defeated by Jimmy Carter and Walter Mondale, 297 to 240 in the Electoral College and 40.8 million to 39.1 million in the popular vote.

Rather than Joe Biden-Kamala Harris, could the Democrats’ fall ticket be Hillary Clinton-Gavin Newsom? Could this scenario play out again in the future?

It certainly is not impossible. Actually, when you think about it, it sounds quite possible.