Rep. Mark Sanford (R-S.C.) hugs his sons after addressing his supporters in Mount Pleasant, S.C., on Tuesday. (Wade Spees/Associated Press)
Columnist

Over and over again, Rep. Mark Sanford (R-S.C.) has warned that President Trump is turning his party into a “cult of personality.”

On Tuesday night, Sanford proved it is true.

The staunchly conservative former governor, who at one time had been considered a potential presidential contender, was defeated in a Republican primary by a first-term state representative who had made fealty to Trump the defining issue in the race.

His loss to Katie Arrington, Sanford told me Wednesday morning, will send a strong message to other Republicans about the consequences of calling out Trump for his apostasies on the things conservatives claim to hold dear — from fiscal responsibility to free trade. Or for pointing out, as Sanford did, Trump’s ignorance about what is in the Constitution and the president’s singular lack of transparency in refusing to release his tax returns.

“They don’t want the tweet that I got last night,” Sanford said. “There’s no motivation like self-motivation.”

The tweet in question was a broadside, delivered just three hours before the polls closed.

“Mark Sanford has been very unhelpful to me in my campaign to MAGA. He is MIA and nothing but trouble,” Trump wrote. “He is better off in Argentina. I fully endorse Katie Arrington for Congress in SC, a state I love. She is tough on crime and will continue our fight to lower taxes. VOTE Katie!”

The Argentina reference was a reminder of the sex scandal that made Sanford a national sensation in 2009. It says something that Republican voters have reached the point where they do not even shrug at the hypocrisy of Trump, who is involved in a legal battle with an adult-film actress with whom he allegedly had an affair.

That tweet probably made the difference, Sanford told me, noting that the results were within a few hundred votes of what it would have taken to get into a runoff with Arrington.

“But I don’t know if the outcome would have been different in the long run, because of the larger tide I was up against,” he added.

Nor is he the first. In Alabama, Rep. Martha Roby has been forced into a July runoff, because Republicans there are still furious that she called on Trump to quit the 2016 campaign after the release of a video in which he bragged about sexual assault.

So Republicans will continue to stay silent, rather than challenge Trump — an impulse that, while based on self-preservation, undermines their basic values and their norms.

The very day of the South Carolina primary, Sen. Bob Corker (R-Tenn.) — who is not running for reelection — taunted his Senate colleagues for their reluctance to “poke the bear” and take more authority over tariffs. And in the House, moderate Republicans fell two signatures short in their efforts to use a procedure known as a discharge petition to force a debate on legislation to protect young undocumented immigrants who were brought to this country by their parents.

Meanwhile, in Virginia, Republicans gave their Senate nomination to conservative extremist Corey Stewart, who, as he celebrated his victory, railed in Trumpian fashion against “criminal illegal aliens,” and added, “by the way, they are animals.”

Forget the Big Tent. There is no longer any room for disagreement. “We are the party of President Donald J. Trump,” Arrington declared in her victory speech.

Until he took on Trump, Sanford had been one of the most remarkable survival stories in modern politics.

A quirky and combative governor, he became nationally known in 2009, when he disappeared to Argentina to see his mistress while claiming to be hiking the Appalachian Trail. But he refused to resign as the ensuing scandal destroyed his marriage, spawned impeachment proceedings and saddled him with the largest ethics fine in South Carolina history.

Sanford’s final year in the governor’s mansion not only turned out to be his most productive but also laid the groundwork for him to return to public life in 2013 and win his old congressional district in a special election. In 2016, as Trump won the South Carolina’s 1st Congressional District by 13 points, Sanford coasted to reelection with a 22-point victory.

Some of his baggage surely lingered. Republican officials say their private polling showed that Sanford was struggling, in particular with female voters.

But the main factor in his defeat was that the Republican base was turning on him in favor of Trump. Sanford says he tried to explain why he had his differences with the president, but South Carolina’s Republican voters had no interest in hearing them.

“The idea of some allegiance not to the Constitution, but to the president, was not what I signed up for,” Sanford said.

In the era of Trump, that has become the only loyalty that matters.