Aaronson is far from the first promising young American to get a chance to shine in front of the full squad, as he joins likes of Paxton Pomykal, Miles Robinson, Sergino Dest, Jackson Yueill and others to join their first senior camp in 2019.
It's not by accident.
"Along similar lines of Paxton and Miles, it's bringing guys in and exposing them to the senior national team," Berhalter told reporters on a media conference call Wednesday. "[Aaronson is] a guy we want to see how he reacts, takes in information. It's already beginning to work with these players so, eventually, when they come up, they're used with how we work. He [was born in 2000], he's an extremely young player. It's been great watching him, we think he's ready for an opportunity after performing really strongly with Philadelphia."
Aaronson, Pomykal and Robinson are expected to be three key players for this current U-23 side for the 2020 Olympics cycle. After Pomykal and Robinson got their first senior call-ups in September, they were not included on this latest October squad, and are expected to link up with the U-23 camp next week while Aaronson jumped from the U-23s to the senior side.
"We're purposefully integrating U-23 players into the full squad, to give them experience and exposure to a high level," Berhalter said. "I think it's an excellent group, there are some very good players in that team. It's a deep team, when you look at the competition for starting XI positions in that group, it's very good."
Aaronson has made 27 appearances, 24 starts, for the Union in 2019, who are tied for second place in the Eastern Conference. The MLS Rookie of the Year candidate has added three goals and two assists.
"The one thing I like about Brenden is that he's playing for a team that's competing for the top of the East. That's exceptional," Berhalter said. "He's been playing all year, he's consistent."
Berhalter believes the kind of open door between the U-23 team and senior side for young players is valuable.
"Miles Robinson is a good case," Berhalter said. "We wanted to bring him around our group, we think he's had a good MLS season, and it was time to expose him to a higher level of competition. He's a guy that's right on the cusp of the full national team, but now for him to go back to play with the [U-23's], to lead by example and help other players with his experience.
"There's good synergy between the two teams, there's good communication between the coaching staffs," Berhalter added. "We think it's important for that team to be successful."