Dressel wrapped up his emotional return to the US trials on Saturday, following up his 50m free victory on Friday with another win after his lengthy break from the sport.
Dressel seized control with his trademark explosive start, led at the wall and won in 50.19sec, with 17-year-old Thomas Heilman second in 50.80.
Heilman had already won the 200m fly to become the youngest US male swimmer to book an Olympic berth since 15-year-old Michael Phelps and 17-year-old Aaron Piersol competed at the 2000 Sydney Games.
He flew home in the outside lane one to edge 21-year-old Dare Rose by four-hundredths of a second.
"This is truly the hardest part," Dressel said of the pressure-cooker US trials, where only the top two finishers in each event can secure an individual Olympic berth.
"It's tough to make the team here, and that's how it should be," said Dressel, who won five gold medals at the Tokyo Olympics to confirm his superstar status but abruptly stepped away from the sport in 2022.
"I think I've felt every emotion that I'm capable of," Dressel said of the rollercoaster nine-day trials, held this year in the stunning, potentially intimidating atmosphere of Lucas Oil Stadium, home of the NFL's Indianapolis Colts.
"It's tough. So really the motto is one stroke at a time. You've got to turn the dial on, then turn it off and just when you can go to bed. So I'm happy to be done," said Dressel, who has been cheered on this week by his wife, Meghan, with their four-month-old son, August, along for the ride.
Ledecky's fourth victory of the week, in the 800m freestyle, takes her back to where her Olympic journey began, with an upset triumph at the age of 15 in the 2012 London Games.
Ledecky, the world record-holder who owns the top 16 times ever in the event, clocked 8min 14.12sec. As in the 400m free, Paige Madden was second to Ledecky, shattering her personal best with a time of 8:20.71.
In Paris Ledecky will be the favorite to become the first woman in any sport to win Olympic gold in the same event four times.
Michael Phelps the only swimmer to win the same event at four straight Games, the 200m individual medley in 2004, 2008, 2012 and 2016.
Douglass treble
Kate Douglass added an impressive victory in the 200m individual medley in 2min 06.79sec to her 100m free and 200m breaststroke wins this week.
Alex Walsh was second in 2:07.86 and the pair head to Paris aiming to improve on their performances at the pandemic-delayed Tokyo Games, where Walsh took silver and Douglass earned bronze behind Japanese gold medallist Yui Ohashi.
"I feel like the goal coming into this meet was to try and win all three events, but you know, I didn't really think I was going to be able to achieve that," Douglass said. "So I'm really happy I did."
Walsh finally secured her Paris berth on the penultimate night of the trials, joining her sister Gretchen who clocked a world record in the semi-finals on the way to winning the 100m fly.
"I didn't know if I was going to make it to Paris after she made it," said Alex Walsh, who competed in Tokyo as Gretchen missed out. "This is a dream we've been dreaming for so long."
