Sen. Ben Sasse (R-Neb.) speaks to voters near Central City, Neb., in early June. “I can’t support someone that I don’t think would take the oath of office in good faith,” he has said of Donald Trump. (Ben Terris/The Washington Post)

One afternoon in the spring of 2010, a few years before he made a name for himself as Donald Trump’s most prominent Republican antagonist, Ben Sasse went to his former high school to wrestle.

He was a college president at the time, not yet a U.S. senator. His old coach had asked him to give the team a pep talk; Sasse, then rounding the corner on 40, decided to throw on the gear and see whether he could still hold his own.

He couldn’t.

Lunging at the ankles of his more agile sparring partner, Sasse fell and caught his ring finger on the mat, snapping the bone backward and tearing the ligaments. A spectator who saw the finger jutting out at a horrific right angle ran out of the room to throw up. It still hurts, Sasse says, when it rains.

His wife, Melissa, wishes she had known his plan, so she could have talked him out of it. Sometimes, she says, he needs reminding that not every fight is worth it. “He’s got a need for competition,” she said recently. “Also he’s an idiot.”

Today, freshman senator Ben Sasse of Nebraska remains the only Republican in the U.S. Senate who has consistently, and vocally, opposed his party’s nominee.

For much of the rest of his party, it’s been a tortured, up-and-down relationship they can neither quite commit to nor quit. In the days since Trump attacked a federal judge for his Mexican heritage and congratulated himself for guessing that a mass shooting had links to Islamic fundamentalism, many Republicans have been looking for ways to distance themselves from a candidate they had only just recently embraced.

Some are splitting hairs — saying they will “support” Trump but not “endorse” him; they will endorse him but condemn his rhetoric. Sen. Susan Collins of Maine and Sen. Jeff Flake of Arizona have said they can’t support their party’s nominee but haven’t fully closed the door; Sen. Mark Kirk of Illinois broke with Trump, but previously had said he’d support him; even former arch-antagonist Lindsey Graham is having “cordial” conversations with him. Many others, clearly perturbed, spent last week refusing to utter Trump’s name, telling reporters they won’t discuss him until after the election — or, if that didn’t work, realizing that they were suddenly late for a meeting.

All this drama coming so soon after many startling reversals — Marco Rubio, who once called Trump a “con man” now saying he’d be "honored” to speak at his convention; Paul Ryan, who dissed the nominee by withholding his support, ultimately endorsing him.

Only Sasse, among Senate Republicans, has not budged and maintains he never will. If there will be a moral high ground to claim after 2016, he may be standing on it by himself.

Sasse at the U.S. Capitol in November. His anti-Trump stance has drawn skepticism and resentment from fellow Republicans — but no small measure of attention from the media and like-minded conservatives. (Bill Clark/AP)

“I can’t support someone that I don’t think would take the oath of office in good faith,” he said. As a conservative opposing Trump from the right, Sasse (pronounced “sass”) has earned accolades from the small but vocal Never Trump crowd. He fielded calls from Weekly Standard scribe Bill Kristol and former standard-bearer Mitt Romney urging him to run as an independent. (Thanks, but no, he said).

Though Sasse doesn’t face reelection for another four years, his stance has threatened to leave him without a party. At their state convention last month, Nebraska Republicans passed a resolution in opposition to a third-party campaign that was seen as a rebuke of Sasse. Even after a week when Trump appeared to be hemorrhaging support, Sasse’s absolute opposition still carries a risk in a partisan culture that prizes being a team player. If Trump wins the presidency, he runs the risk of being ostracized. If Hillary Clinton wins, he could be blamed.

Sen. Ben Sasse (R-Neb.) discussed his conservative identity at the 2016 Conservative Political Action Conference. (C-SPAN)

“What is he doing?” Ben Nelson, Nebraska’s former Democratic governor and senator, mused recently. “There’s certainly all kinds of speculation about it.”

Does he see a path that other conflicted Republicans can’t find? Is he positioning himself for a 2020 presidential run? Or, is it possible that Sasse is simply standing on principle, that he sees a fight worth having, even if it’s one he might lose?

On a recent early morning in the central town of Hastings, Sasse stood in a middle school parking lot rubbing Vaseline on his nipples.

“This is the most glamorous part of the race,” he said, before limbering up for the town’s half marathon. Sasse, 44, is the kind of guy who keeps track of his monthly push-up count; Trump once jabbed over Twitter that he looks more like a “gym rat than a U.S. Senator.” With a toothy grin, narrow eyes and a close-cropped haircut, he could pass for a Romney son. A “reluctant runner,” he took up the sport to spend time with his daughters, Alex and Corrie.

Sasse put on his headphones and fired up a playlist of Tom Petty, the Lumineers and a podcast from conservative pundit Matt Lewis. The audio would have the benefit of blocking out potential hecklers.

“I’d say there’s a 14 percent chance that someone yells at me,” he said.

Sasse and his daughter Corrie, in the gray shirt, start the Half Hastings footrace in Nebraska. A former wrestler and “reluctant runner,” the senator is the kind of guy who keeps track of his monthly push-up count. (Ben Terris/The Washington Post)

Just the night before, a stranger — who had clearly had a few — ambled up to the senator while he ate dinner with his family. The man declared that Sasse’s resistance to Trump amounted to support of Hillary Clinton. Sasse told him he dislikes both candidates equally and hopes to send a signal that Americans are not okay with these kinds of options.

“I don’t care about any of that s---,” the man snarled.

Most of the yelling at Sasse — the rare senator with a natural feel for social media — takes place online. In January, he tweeted a series of questions toward Trump, asking for his thoughts on health care, guns, executive authority, tax hikes and whether he had repented for his “many affairs w/ married women.” In February, he wrote an open letter to Trump voters on Facebook: “I’m as frustrated and saddened as you are about what’s happening to our country. But I cannot support Donald Trump.”

Last month, Sasse walked down to the Platte, a broad, muddy river surrounded by switchgrass and cottonwood trees, for a little social-media confessional. His “Open Letter to the Majority of America” was either heartfelt or hokey, depending on your level of cynicism, describing a lineup of voters from central casting — evangelical mom, union Democrat, middle-aged Republican guy — who had approached him in a Walmart to vent about the political system. What the country craves, Sasse concluded, was a third option.

Trump chimed in on Twitter to call him “totally ineffective” and suggest that Nebraska find a better senator. Mobs of Trump-supporting Internet trolls have called him a beta-male or a fake conservative.

“Apparently I’m also Jewish,” the Lutheran noted with a shrug.

Sasse doesn’t mind ridicule, but there have been times when he’s feared for his family’s safety. They recently found strange letters in their mailbox.

“It said something like, ‘There are a lot of us, and we are voting for Trump,’” said Melissa, waiting for Sasse at the finish line. “It’s unsettling. I just don’t like people knowing our address.” She’s considering applying for a gun license, just in case.

Sasse won his seat in 2014 by being both a Beltway insider who knows how the game is played and a tea-party-friendly conservative railing against that very game. With degrees from Harvard and Maryland’s St. John’s College and a history PhD from Yale, he went to work at the Justice Department and was appointed by President George W. Bush as an assistant secretary in the Department of Health and Human Services.

Sasse at the American Conservative Union conference in Maryland in March. “The only way you can do this job well is if . . . you act like you had no intention of running for reelection,” he said recently. (Gary Cameron/Reuters)

Like many politicians, he’s more likely to tout his private-sector work, as a consultant for troubled businesses and later president of Midland, a liberal arts college in his home town of Fremont, Neb.

On the night of his 2014 election to the Senate, he gave a speech calling out politicians for their “constant finger-in-the-wind attempts to pander” and warning that “doing the right thing for tomorrow’s voters will not always seem popular today.”

Easy to say, until you do something unpopular.

“He’s really out of step with the majority of Nebraskans on this one,” said Phil Young, a political consultant who worked for one of Sasse’s primary opponents. (Trump won 61 percent of the vote in the May primary that drew a low turnout after Ted Cruz dropped out.) “But I don’t think he cares. He’s going to say what he wants to say, regardless of whether it represents his constituents.”

The other problem: Sasse is standing up to Trump without offering an alternative. He says he never considered running himself, citing family obligations. (He and his wife home-school their daughters and young son.) He had hoped a former military leader, perhaps James Mattis or David Petraeus, would offer a “Dwight Eisenhower-type choice.”

Without a conservative third-party campaign, Sasse looks to some less like a warrior in the ring and more like an agitator in the stands.

“He’s carrying on like a professor, telling the world how things should be,” said Bob Krist, a Nebraska state senator. “Either get out in front and lead, or be part of the process that you have been elected to be a part of.”

Sasse responds that he believes a majority of Nebraskans — perhaps even a majority of Republicans — share his concerns about Trump’s disregard for the Constitution and various temperamental issues. Plus, what’s the point of being a senator if you can’t take a stand you believe in?

“The only way you can do this job well is if, for 4½ years of a six-year term, you act like you had no intention of running for reelection,” he said. He’s never had a job for more than five years anyway.

Sasse and his daughter Alex pack a box of groceries at a mobile food bank in Central City, Neb. He’s been criticized for urging a third-party campaign without volunteering for it, citing obligations to his family. (Ben Terris/The Washington Post)

At the same time, he’s garnered an outsize amount of press for a senator who ranks 99th in seniority. If Trump turns into a long-term black eye for the GOP, Sasse will be one of the very few unblemished. There are worse spots from which to launch a future campaign.

None of this is lost on a man who was shrewd enough to run as both an insider and outsider. And while Democrats may like him today for his anti-Trump stance, he could turn into a nightmare for them if he ever decides to run. He stands to the right of most Senate Republicans, but with a nice-guy personality that would be hard to demonize. He’s Ted Cruz with a winning personality. He’s Scott Walker with a PhD. And for better or for worse, he’s the anti-Donald Trump.

After finishing the half marathon with Alex in under two hours, he loaded the family into their red 2006 Chevy pickup to hit some constituent events — packing boxes at a food bank in Central City, then delivering a speech about the current political climate to a “future leaders” group. Afterwards, he acknowledged his limitations as a political seer.

“I thought for a long time the political parties would come apart — but, I’ll be honest, I was wrong about one really significant thing: I really did think the Democrats would come apart first.”

The last stop of the day was the Cattlemen’s Ball, near the tiny town of Princeton, where hundreds of ranchers gathered to eat prime rib and drink beer. But when Sasse pulled into a parking spot and turned off the truck’s engine, the AC fan continued to run. If he let it go, it would drain the battery.

He popped the hood and discovered a malfunctioning fuse. He needed to take it out. But with what?

Sasse reached into the back seat and grabbed one of the suits he wears in Washington. There he found what he needed — a lapel pin, featuring both his state seal and the Stars and Stripes, a symbol of his duties as a Nebraskan and an American.

Unfortunately, no amount of futzing with the pin would make the fuse budge. Somebody would soon come by with pliers, and Sasse would just have to wait.