As GOP operatives race to the spin room to tout their candidates’ performance in the Milwaukee debate, President Reagan’s 11th Commandment — “Thou shalt not speak ill of other Republicans” — is having its moment. All eight contenders embraced its enduring wisdom, setting their sights not on each other or the absent President Trump, but President Biden and the Democrats.

Like “My Way,” which Reagan’s friend Frank Sinatra joked he “stole,” the 40th president made the 11th Commandment his own, but he didn’t write it. The rule was born out of another contentious GOP primary, when California’s party chairman, Dr. Gaylord Parkinson, decreed that Reagan and his two rivals for the gubernatorial nomination should avoid inflicting fatal wounds on the eventual nominee.

“I believe in the 11th Commandment,” Reagan said after weathering attacks by his opponents at a convention, “and I pledge to support the party’s nominee.” Note that Reagan said only that he believed in the rule, not that he’d follow it to the letter, a loophole that he’d need a decade later.

This year, the RNC sought to extract an 11th Commandment-style commitment to support their party’s nominee. All the candidates at Milwaukee agreed to sign the pledge, but Mr. Trump balked. “I can name three or four people that I wouldn’t support for president,” he told Newsmax last month. “So right there, there’s a problem.”

Mr. Trump’s stance is a departure from Reagan and Gaylord, who wished to avoid fratricide and target California’s incumbent governor, Democrat Edmund “Pat” Brown. Republicans at Milwaukee embraced this strategy and targeted the Democrat whose job they hope to win, Mr. Biden, managing to seem like they were itching to confront him rather than cowed by Mr. Trump’s commanding lead in polls.

Even Governor Christie, one of Mr. Trump’s fiercest critics, hewed to the spirit of the 11th Commandment and signed the pledge. “The most important thing,” he told Fox News last week, “is to be on the stage so our voters get to make an informed choice about who can beat Joe Biden.”

On Tuesday, Speaker McCarthy, the highest ranking Republican in the government, also invoked the spirit of the 11th Commandment. Mr. Biden, he told Larry Kudlow on Fox Business, “is out of tune, out of touch, and I’m really going to watch this debate looking for the individual who lays that out best, making the argument against Biden economics and for a more prosperous America focused on America first.”

That focus was on display from Tuesday’s very first question, which Governor DeSantis of Florida used to go after Mr. Biden. Mr. Trump’s name was not mentioned until Governor Haley of South Carolina talked about his administration 15 minutes in, and when it came to  the topic of Mr. Trump, Mr. DeSantis dragged the focus back to the 11th Commandment.

 “This is not about January 6th,” Mr. DeSantis said. “It’s not about January 20th. I know what the Democrats would like [it] to be. They want to talk about these other issues, but we have to focus on your future. … Republicans, we’ve got to look forward.” Mr. Pence agreed, noting that he used Reagan’s Bible when swearing his oath to upload the Constitution.

 Mrs. Haley toed the same line, noting that voters don’t want to see a 2020 rematch and remarking that Mr. Trump is “the most disliked politician in America” only enroute to buttressing her next sentence that Republicans “cannot win a general election that way.”

Reagan’s embrace of party unity brought him victory in the 1966 California primary with over 64 percent of the vote and, with a united GOP behind him, he trounced Brown by more than 15 points. In 1980, he would oust another Democratic incumbent, President Carter, again winning in a landslide, but a funny thing happened on the way to the White House.

That thing was Watergate, which led to President Nixon’s resignation and the ascension of President Ford, who had been confirmed as vice president by the Senate to fill the vacancy left by Vice President Agnew’s resignation, making him the first man to achieve the presidency without being elected to either office — and, therefore, vulnerable.

In the 1976 primary, Reagan decided to challenge Ford for the nomination, but knew he needed the same united party he had enjoyed after the 1966 face-off. The chairman of Reagan’s Florida campaign, L. E. Thomas, recalled that he “begged” him to “take the gloves off,” but “Gentleman Ron” refused.

“‘Tommy, I can’t do it,'” Thomas recalled Reagan saying, rejecting slinging mud at Ford. “He originated the 11th Commandment, and he said, ‘I cannot attack him.'” Thomas saw the turning point as the moment a “crowd screamed and jumped up and down” when Reagan said he’d fire Secretary Kissinger. Reagan realized he’d “struck a nerve,” and Thomas told him to “do more of it.”

After losing two-to-one to Ford in Massachusetts, Reagan began sinning against the 11th Commandment, praising Ford’s decency but saying he lacked “vision and leadership.” The change delivered Reagan a victory in North Carolina, handing Ford the first primary loss for a sitting president since President Truman in 1952.

Reagan began steamrolling to victories and the 1976 Republican nomination remained undecided right up to the convention. Ford prevailed, but violating the 11th Commandment wounded the party and Carter ended up winning a squeaker by 2.1 percent.

In 1980, Reagan again faced a primary, but this time, he concentrated his sharpest barbs for Carter. The 11th Commandment prevailed and enabled him to unify the party by choosing his chief rival, President George H. W. Bush, as his running mate and capturing the White House.

Consultants and pundits spend hours advising candidates to follow complex paths to victory and whittle words into swords, but the best strategy remains the simple 11th Commandment. The Republicans at Milwaukee respected its spirit on Wednesday night, and by doing so, boosted their party’s chances of winning this one for the Gipper.