The Republican presidential candidate who really came into focus at the first debate is the governor-turned-diplomat, Nikki Haley of South Carolina. She confronted the most aggressive figure in the GOP field, Vivek Ramaswamy, on the strategic choices that are likely to be at the center of any Republican administration.

Mr. Ramaswamy emerged as the winner of the debate on the Fox News stage, according to Fox’s own poll. He certainly managed to keep the microphone and came up with many quotable lines. He reiterated his vow to pardon the 45th president. Yet, being Trumpier than the frontrunner can only carry a candidate so far. 

What Ms. Haley did was to revive the principled, idealistic, yet factually based rubric that Reaganites once held in American politics. She forced voters to look for a potential winner who would reconsider a pre-Trump Republicanism. She might have connected with heavy donors disappointed by Governor DeSantis.

While a fellow Palmetto Stater, Senator Scott, delivered a lackluster performance, the former South Carolina governor displayed considerable debating skills. In and of itself, that’s not surprising, given her performance as President Trump’s ambassador at the United Nations. 

Ms. Haley especially shone on foreign policy as she, more forcefully than any other, challenged the isolationist instincts of Mr. Ramaswamy, who on Wednesday served as Mr. Trump’s doppelganger. Ms. Haley urged the crowd to look beyond the most recent Republican president.

“When you’re looking at the future of America, I think it’s time for a new generational change,” the 51-year-old Ms. Haley said. “I don’t think you need to be 80 years old to go be a leader.” She raised a hand when candidates were asked if they would endorse a convicted Mr. Trump, but she argued it would be difficult for the party to win with the “most disliked politician in America.”

Ms. Haley made her first splash on the national scene when, in the aftermath of a 2015 massacre of nine Black South Carolinian churchgoers, she removed the confederate flag from the state capitol and all government buildings.

Entering the UN headquarters at New York in January 2017, Ms. Haley shocked genteel denizens of Turtle Bay by vowing to “have the backs of our allies and make sure our allies have our back as well.” As for those who don’t side with America, she added with a swagger that became her diplomatic signature, “We’re taking names.” 

Ambassador Haley took a similar attitude in responding to Mr. Ramaswamy’s call to end America’s support of global allies. “He wants to hand Ukraine to Russia, he wants to let China eat Taiwan, he wants to go and stop funding Israel,” she said. “You don’t do that to friends. What you do instead is you have the backs of your friends.”

Ms. Haley chided the Trump administration for adding $8 trillion to the national debt. Despite her anti-abortion position, she said she sees no realistic path to a national abortion ban, which must be approved by 60 senators. With that, she also gave listeners a look at how she would approach the post-primaries general election. 

Other candidates urged more oil and gas drilling. Mr. Ramwassamy dismissed climate change as a “hoax.” Ms. Haley went after multilateralist pacts. Mr. Biden’s favored Paris Accords, she noted, exempts major polluters from restrictions imposed on America.

Climate change is real “but if you want to go and really change the environment, we need to start telling China and India that they have to lower their emissions,” she said. 

Does America spend too much on Ukraine, while Europeans sit on their hands? We spend “less than three and a half percent of our defense budget” on Ukraine, Ms. Haley said, while “11 of the European countries have given more than the U.S.” relative to the size of their economies. 

In her UN days, Ms. Haley often impressed reporters and diplomats alike with her mastery of the soundbite, while critics argued that her command of the details left a lot to be desired. On Wednesday she proved them wrong. Ms. Haley provided a glance into a future Trumpless Republicanism.