By Carl P. Leubsdorf

The Dallas Morning News

It’s 15 months until the next presidential election — time for a round of rumors about the president dumping his running mate.

They arise about this time every four years, though it’s been more than four decades since a vice president was dumped. And in that case, neither the president, Gerald Ford, nor the vice president, Nelson Rockefeller, had been elected, the result of the back-to-back scandal-driven resignations of Vice President Spiro Agnew and President Richard Nixon.

Former UN Ambassador and South Carolina Gov. Nikki Haley launched the latest version of this perennial political parlor game by tweeting, “Enough of the false rumors. Vice President Pence has been a dear friend of mine for years. He has been a loyal and trustworthy VP to the President. He has my complete support.”

What rumors she was referencing remains something of a mystery.

Besides, Trump had just reiterated his support for Pence, as The New York Times’ Maggie Haberman quickly noted. She tweeted she asked the president the previous Sunday if he is thinking of replacing Pence. “No, I’m very happy with Mike Pence,” he replied, dismissing discussions about making a change as “standard.”

In this instance, Trump isn’t far from the truth, though changing running mates often seems discussed more by the political community than by the principals themselves. And it’s almost always dismissed as a bad idea.

After all, a presidential nominee’s first significant act is picking his running mate. Ditching one four years later would be an admission of error, which is why it rarely happens. Besides, any prospective political gain might be offset by attendant political damage.

In addition, most analysts have concluded that vice presidential candidates neither help much in an election — nor cause much damage. The only exception might be a small boost in the VP nominee’s home state.

For example, it’s widely believed that John F. Kennedy wouldn’t have carried Texas in 1960 without Lyndon B. Johnson as his running mate. Of course, Kennedy would still have won the election.

And before Kennedy was assassinated three years later, rumors of replacing Johnson had risen again, in part thanks to the well-known antagonism between him and the president’s brother, Attorney General Robert F. Kennedy. But few believe the Kennedys would have broken up a winning team.

Eight years ago, there was speculation President Barack Obama might improve his reelection chances by replacing Vice President Joe Biden with Secretary of State Hillary Clinton. But the Obamas and the Bidens had gotten quite close personally, and the rumors didn’t go anywhere.

One of the most serious efforts to switch running mates came in 1992, when President George H. W. Bush was facing a difficult reelection fight. Some top advisers including his son, future President George W. Bush, reportedly thought he could boost his prospects by replacing Vice President Dan Quayle with Gen. Colin Powell.

But such a change might have angered GOP conservatives, who backed Quayle more strongly than Bush. And Bush, always loyal to associates, said for three years he would run again with Quayle and characteristically kept his word.

The last time a president ditched an elected vice president was during Franklin D. Roosevelt’s four-term presidency in the 1940s. He did it twice.

Roosevelt’s original vice president, John Nance Garner, was chosen in a 1932 convention deal that enabled Roosevelt to clinch the presidential nomination. The two were never close, and when Roosevelt decided to seek a third term, Garner unsuccessfully challenged him, eliminating himself from the ticket.

Roosevelt chose a liberal favorite, Secretary of Agriculture Henry Wallace. But four years later, party leaders considered him too liberal, and Roosevelt chose Harry Truman, who had come to prominence as chairman of a Senate committee investigating defense profits during World War II.

Ever since, presidents have publicly declared their loyalty to their running mates, even when considering a change. One exception was when President Dwight D. Eisenhower suggested that Vice President Richard Nixon might have a better chance of succeeding him if he moved to a major Cabinet position, like secretary of defense, in a second Eisenhower term. Nixon decided it would be better to stay put.

There are no signs that Trump plans to replace Pence, whose support among religious conservatives was a major 2016 GOP asset. But now that Trump has named two conservative Supreme Court justices and made other policy changes religious conservatives favor, he might not be as important.

The real crunch may come if the Democrats, who hold the first 2020 convention, put a woman on their ticket, which is likely. That might prompt the famously mercurial Trump to reconsider replacing Pence with Haley, or another prominent Republican woman.

Given Trump’s questionable reelection prospects, Haley’s tweet may have been designed to help her stay off the ticket and not damage her post-Trump presidential prospects. The last losing vice presidential nominee to be elected president was FDR, the vice presidential nominee in 1920.

So, even history says the GOP is likely to renominate the Trump-Pence ticket.

Carl P. Leubsdorf is the former Washington bureau chief of the Dallas Morning News. Readers may write to him via email at: carl.p.leubsdorf@gmail.com.