MOBILE, Ala. — As a longtime senator from Alabama, Jeff Sessions did nothing less than legitimize Donald. J. Trump as a credible Republican candidate for president, endorsing him when no other big names did and championing him to conservative voters. As Mr. Trump’s star rose, Mr. Sessions’s rose, too.
But on Tuesday night, as he sought once again to become a senator from Alabama, a job he loved, Mr. Sessions came crashing to the ground — and all at the hands of Mr. Trump, his ally-turned-patron-turned-antagonist-turned-sworn enemy.
Mr. Sessions was soundly defeated in Alabama’s Republican primary, losing to a political neophyte, the former Auburn football coach Tommy Tuberville, whom Mr. Trump had enthusiastically supported while denigrating Mr. Sessions.
With 100 percent of the vote counted, Mr. Tuberville had 60.7 percent of the vote, to 39.3 percent for Mr. Sessions.
“We’ve fought a good fight in this race,” Mr. Sessions said, addressing supporters at a small conference room at a Hampton Inn in Mobile.
“I want to congratulate Tommy Tuberville,” Mr. Sessions said, fighting back tears. “We must stand behind him in November. Doug Jones does not need to be our voice in Washington. He wishes to see the policies of Nancy Pelosi prevail over conservative Alabama principles.”
Mr. Sessions said he had no regrets about his decision as attorney general to recuse himself from the investigation into Russian interference in the 2016 election — an act that infuriated Mr. Trump and turned the president against him. “I followed the law,” he said, adding, “and I saved the president’s bacon in the process.”
Mr. Tuberville will now face Mr. Jones, the most vulnerable Senate Democrat up for election in November. Mr. Jones narrowly defeated Roy S. Moore, a former State Supreme Court justice, in the 2017 special election to fill the seat vacated by Mr. Sessions.
Mr. Tuberville’s victory was the most prominent result in voting across three states Tuesday. In Maine, Sara Gideon easily won the Democratic nomination for Senate and will challenge Senator Susan Collins in November, in what would be one of most closely contested, and expensive, races in the country this year. And in Texas voters in both parties went to the polls to decide runoffs in several House races and Democrats selected M.J. Hegar, an Air Force veteran, to challenge Senator John Cornyn in November.
Few Republicans had tied their political fortunes to Mr. Trump as Mr. Sessions did. As one of the loudest Senate voices for taking a hard line on immigration, Mr. Sessions had few allies among past G.O.P. presidential candidates. Then came Mr. Trump, who not only ran on Mr. Sessions’s agenda but won on it — then brought Mr. Sessions forth from the backbench and installed him in what was supposed to be his dream job: attorney general.
What came next was a one-man cautionary tale about the risks of linking one’s career to a mercurial president to whom loyalty meant everything. Enraged that Mr. Sessions did not block the Russia investigation, but instead recused himself, Mr. Trump made it his mission to humiliate his attorney general. He mocked Mr. Sessions’s Southern accent, hectored him on Twitter and belittled him in interviews — and only after all that did he fire him, days after the 2018 midterms.
When Mr. Sessions decided to try to reclaim his Senate seat, Mr. Trump, after initially resisting, did it all over again, unleashing his brand of personal vengeance to derail Mr. Sessions’s attempted comeback.
In perhaps the most trying stretch of his presidency, with his own poll numbers plummeting, the president made the most of the Republican runoff.
On Monday night, by which point it was clear Mr. Tuberville would triumph, Mr. Trump held a conference call with the candidate and his supporters, during which he again savaged his former attorney general — “He had his chance and he blew it” — and offered Mr. Tuberville a ringing endorsement.
The former coach “is going to do a job like you haven’t seen,” said the president, adding: “He’s going to have a cold, direct line into my office. That I can tell you.”
Mr. Tuberville, addressing his own supporters Tuesday night, accused Mr. Jones of upholding “New York values, Chicago values, liberal Democrat values” while calling Mr. Trump “the best president of my lifetime.”
In Maine, Ms. Gideon, the state House Speaker, fended off nominal opposition from the left, which she largely ignored as she built a record-setting war chest. The race has already become the priciest Senate campaign in Maine history, thanks to a fund-raising surge from liberals angered by Ms. Collins’s support for the nomination of Brett M. Kavanaugh to the Supreme Court two years ago.
Ms. Collins’s prospects will weigh heavily on the balance of power in the Senate, where Democrats are seeking to pick up the three seats that would give them a majority under a President Biden. Ms. Collins, who is considered one of the most vulnerable Senate Republicans, is facing perhaps her most difficult campaign as she seeks a fifth term.
Ms. Collins is trying to build a coalition that includes both Mr. Trump’s enthusiasts and detractors at a time when centrists like her are growing scarce.
Mr. Sessions had spent much of his campaign urging Alabama voters to remember that he was running against Mr. Tuberville — not Mr. Trump.
“The president has a right to speak up, but the president is not on the ballot,” Mr. Sessions told reporters after voting on Tuesday in Mobile, Ala., while his granddaughters, wearing red Sessions campaign T-shirts, stood off to the side. “He’ll be on the ballot in November, and Alabama is going to vote for him, and I will be voting for him. But Tommy Tuberville is on the ballot now.”
Yet even as he sought to isolate his race from the top of the ticket in one breath, the former attorney general all but acknowledged in another that Republican nominating contests have become loyalty tests to Mr. Trump.
“My opponent, at age 65, never lifted a finger for Donald Trump, never said he was a Republican in the first 65 years of his life,” Mr. Sessions said. “Never said he was a conservative. Half the time he didn’t even vote — we don’t know if he actually voted for Donald Trump or not in the last election.”
As he did for much of the final stretch of the runoff, Mr. Tuberville avoided reporters on Tuesday and let Mr. Trump’s endorsement speak for his candidacy.
Many who cast their votes in Mr. Sessions’s precinct on Tuesday morning spoke fondly of the former attorney general. Kay Rehm, 69, said she voted for Mr. Sessions “mainly because he is so moral and ethical.”
“We know what we’re getting in Senator Sessions,” Ms. Rehm said. “He’s been vetted, he’s been in government for over 30-something years. I personally have nothing against Tuberville, but we don’t know anything about him.”
Ms. Rehm said she found the president’s disdain for Mr. Sessions “a little disappointing, but Trump can be like that, God bless him.”
But Mr. Trump’s strong support had always been expected to provide a huge lift for Mr. Tuberville. “The president has endorsed Coach Tuberville because he knows Tommy will stand up for America and not be controlled by the deep state and the big money lobbyists,” said Perry Hooper, a former state representative in Montgomery.
In Texas, Ms. Hegar, a former Air Force helicopter pilot who had the support of Senate Democrats, defeated State Senator Royce West in a Democratic runoff to determine who will take on Senator John Cornyn.
Mr. Trump scored a victory in an open West Texas House seat, where his preferred candidate, the former White House doctor Ronny Jackson, won a runoff.
In the race for the seat currently held by Representative Will Hurd, who is not seeking re-election, Mr. Trump and Senator Ted Cruz were on opposite sides of the runoff. The president offered a late endorsement of Tony Gonzales, the establishment favorite, while Mr. Cruz backed Raul Reyes, a more conservative candidate. With 95 percent of precincts reporting by late Tuesday night, Mr. Reyes had a 132-vote lead.
The most surprising news Tuesday came in a contest that won’t even be decided until next month. Shortly before he was to debate his primary opponents, Steve Watkins of Kansas, a first-term Republican congressman, was indicted on felony charges related to whether he voted illegally in 2019.
In terms of determining the balance of power in Washington, though, no race on Tuesday may have been more consequential than the Maine primary. The Senate race there is one of a handful that could determine control of the chamber, where Republicans have a majority, 53 to 47.
Ms. Gideon has already raised nearly $23 million, much of it from Democrats who are angry at Ms. Collins for confirming Justice Kavanaugh and not taking a harder line against Mr. Trump.
And now that Ms. Gideon is officially her party’s nominee, she will receive $3.7 million, which has effectively been sitting in escrow for the Democratic nominee since Ms. Collins’s Kavanaugh vote.
While she has been outraised in the first half of the year, Ms. Collins, who has raised over $16 million so far, has demonstrated an ability to keep closer pace with her opponent than some of her Republican colleagues. Both candidates will also be helped by multimillion dollar ad campaigns from party super PACs in a race that has already turned negative.
Early polls point to a competitive race in a state that has become politically bifurcated between a more conservative and rural north and a liberal-leaning and more densely populated south.
Ms. Collins has deep roots in northern Maine, where Mr. Trump enjoys a strong following. She did not support his candidacy in 2016, and has not said how she will vote in November. She did, though, recently tell The New York Times that she will not campaign against former Vice President Joseph R. Biden Jr., her onetime Senate colleague who is Mr. Trump’s rival for the presidency.