Maya DiRado celebrates her win in the 200-meter individual medley Wednesday night. DiRado, a first-time Olympic, also qualified in the 400 IM at the U.S. swimming trials in Omaha. (Jonathan Newton/The Washington Post)

There is no ambiguity at the U.S. Olympic swimming trials. Black is black and white is white, and if you’re looking for judgment calls, go to gymnastics or diving or dressage. The judge here is the clock, and it can be swayed neither by reputation nor pedigree. Swim fast, and here’s a ticket to Rio de Janeiro. Have a bad day, and sorry, no do-overs. Here’s a ticket home.

As the final three days of this meet approach, then, a new group of brazen, undeterred swimmers have stared down not only the clock but the swimmers on the blocks beside them, some of them heroes as they grew up. This is, we know, the last Olympics for Michael Phelps, the most decorated and famous athlete the sport has produced. Just as important, though, it is the first Olympics for 21 of the 33 swimmers who have qualified for Rio following Thursday night’s finals.

“USA Swimming’s in a bit of a transition phase, from old to new, if I can say it like that,” said Caeleb Dressel, a 19-year-old Floridian who placed second to defending gold medal winner Nathan Adrian in the 100-meter freestyle final Thursday night, making the team. “The youngsters are up and coming, and it shows this meet. We’ve had a ton of new Olympians. It’s been awesome. It’s probably why the place is sold out. I think people knew what was coming. It’s a bunch of youngsters taking over.”

Dressel is just one of the swimmers whose story will be told heading into the Games. Others surged forward Thursday night when Josh Prenot, a 22-year-old who goes to the University of California, emphatically won the 100 breaststroke with an American record mark of 2:07.17. The other swimmer to make the team in that event: Kevin Cordes, who earlier in the meet seized his own spot on the team with a victory in the 100 breaststroke.

Leah Smith, a swimmer the University of Virginia, hugs Katie Ledecky after the 400-meter freestyle finals. Smith earned spots in the 200 and 400 freestyle and the 4x200 relay. (Jonathan Newton/The Washington Post)

“I didn’t feel like waiting another four years,” Prenot said. “So the pressure was on.”

There is, now, a new pressure — swimming and succeeding in the Olympics. Cammile Adams, a 2012 Olympian, won the 200-meter butterfly in 2:06.80, with newcomer Hali Flickinger taking second over another potential first-timer, Alexandria’s Cassidy Bayer. Flickinger’s attitude about that?

“I don’t plan on stopping here,” Flickinger said. “I plan to get faster for Rio.”

So add Flickinger to the list of characters who appear, to some degree, every four years.

“That’s going to happen every trials,” said 12-time Olympic medalist Natalie Coughlin, who failed to make the team in the 100 freestyle Thursday night and has one more chance, in the 50 free over the weekend. “It happened last time. It happened the time before. That’s just the natural progression.”

But with 24 spots still up for grabs, there is the potential for this to be a more significant progression. The last two U.S. swim teams, in 2008 and 2012, included 23 and 25 first-time Olympians, respectively. In six events, the top two swimmers — the two who earn berths on the team — both have been newcomers: Lilly King and Katie Meili in the women’s 100 breaststroke, Olivia Smoliga and Kathleen Baker in the 100 back, Maya DiRado and Melanie Margalis in the 200 individual medley, Ryan Murphy and David Plummer in the men’s 100 back, Cordes and Cody Miller in the 100 breaststroke, and Chase Kalisz and Jay Litherland in the 400 IM.

Kathleen Baker leaps into the arms of Olivia Smoliga after they earned their first Olympic berths in the 100-meter backstroke Tuesday in Omaha. Smoliga was first, Baker second. (Jonathan Newton/The Washington Post)

“All the guys know that there’s a new era that’s going to be ushered in,” said Dave Marsh, who coaches an elite club team in Charlotte and serves as the women’s head coach for the Olympics. “What you want to do is have it be ushered in at a very high level. . . . There’s a natural, really, clash of the titans that’s happening here between the older guys and the younger guys.”

Within that, there is celebration for all of these new faces as they make the team here. But there will be expectations later this summer, when they arrive in Rio.

“I love it,” Smoliga said. “I’m glad there is pressure on me. I feel as though I perform my best when stakes are high. . . . I love the pressure, I love the extra stress, and it’s just an honor to walk in their footsteps and to be kind of handed down that responsibility. I’m ready for it.”

If the United States is to uphold its normal standard in the pool in Rio, Smoliga can’t be alone in that self-assessment. In each of the past six Summer Olympics, Americans have won more swimming medals than any other country, dominating every time. Phelps, Adrian and Katie Ledecky will be among the previous gold medalists who will be trying to lead the way again. But for the numbers to add up — the United States has won at least 26 swimming medals in each of those past six Games — some first-timers will have to contribute.

“There have been some times where I was kind of second-guessing to see if we had really exciting kids that were ready to step up and fill our shoes when we leave,” Phelps said. “But I see that more and more in the sport every day. I might not know half of the team, but by the end I have a feeling I will know the whole team.”

That’s where the fan base sits now, just more than a month from the start of the Olympics. The stories, over that time, will come — how King grew up in an Indiana pool with just four lanes, filled with 35 kids (“Do the math; it’s not a lot of room to swim,” she said); how DiRado made the Olympics for the first time but will retire from the sport after Rio so she can take a management consulting job; how Litherland is one of three swimming triplets; how Cordes moved to Singapore to train.

The story here, though, is all of them, as a group, pushing out former Olympians and their medals, intending to become an old guard all their own.

“I couldn’t have predicted when it was going to happen,” Adrian said. “I knew it was going to happen, just with the aged being pushed out. That’s the name of the game. Just trying to keep up.”