The Tennessee Senate Republican primary may have taken a competitive turn in its final weeks, but Bill Hagerty proved that for red-state candidates in the Trump era, there are still few things more valuable than the endorsement of Donald J. Trump himself.
On Thursday, Mr. Hagerty, 60, who served as the president’s first ambassador to Japan, trounced 14 other candidates in the primary to succeed the retiring Senator Lamar Alexander.
Mr. Hagerty thanked the president in a victory speech from his hometown, Gallatin, with Senator Marsha Blackburn of Tennessee and Senator Tom Cotton of Arkansas joining him onstage.
”I have a very special person to thank — I just got off the phone with him backstage,” Mr. Hagerty said. “That’s President Donald Trump.
“You know, President Trump has had my back since before the beginning of all of this,” he went on. “Thank you for being the inspiration to me, President Trump.”
The race had tightened in its homestretch, with an upstart candidate, Manny Sethi, riding a wave of grass-roots enthusiasm as he positioned himself as the field’s true conservative and most committed ally of the president, earning the support of prominent conservatives like Senator Ted Cruz of Texas and Senator Rand Paul of Kentucky. Mr. Sethi, 42, an orthopedic surgeon, had for months attacked Mr. Hagerty for his background in private equity, longtime friendship with Senator Mitt Romney of Utah and support from the Tennessee Republican establishment.
In the end, it wasn’t enough. Mr. Trump had endorsed Mr. Hagerty before he even entered the race. When skepticism arose about Mr. Hagerty’s commitment to the tenets of Trumpism, Mr. Hagerty squelched it simply by promoting that endorsement even more.
“It’s not as if there was any huge philosophical difference between Hagerty and Manny,” said Stephanie Chivers, a longtime adviser to Mr. Alexander. “So I really believe that Trump’s endorsement made the difference.”
The race was one of the nastiest in recent Tennessee history. As budding enthusiasm for Mr. Sethi became reflected in the polls, Mr. Hagerty went intensely negative. His campaign claimed in television ads that Mr. Sethi’s $50 donation to a Democratic candidate via ActBlue, a liberal online fund-raising platform, was evidence that Mr. Sethi could not be trusted to defend the American flag. He consistently mispronounced his opponent’s name as “Set-ee,” as if to remind voters of the physician’s Indian heritage.
The misleading attacks went both ways: In a web ad, Mr. Sethi tried to link Mr. Hagerty to the Black Lives Matter movement by highlighting his position on the board of a firm that had issued statements in support of it. He referred to Mr. Hagerty as “Mitt Romney’s guy” in ads and speeches, even as Mr. Hagerty made his criticism of the Utah senator clear — a reflection of what now counts as a politically damaging attack in Mr. Trump’s Republican Party.
Mr. Hagerty is unlikely to have trouble defeating his Democratic opponent, Marquita Bradshaw, a Memphis-based progressive activist, in November, as polling suggests that Tennessee remains squarely within Trump country. But his likely ascension to the Senate is an endpoint of sorts to the moderate tenor that has long defined Tennessee Republicanism, of which Mr. Alexander was among the last representatives.
“This may well be the end of an era,” said Keel Hunt, the author of two books on Tennessee politics.