Realistically, this is where so much of the player pool sits. Pochettino has designed it that way. Just last camp, he said there were between 30 and 35 players in consideration. At least 15 of those players fit into this group.
Starting with goalkeepers, anyone not named Freese or Turner is in this spot fighting for that third spot. In terms of defenders, there is a competition going on for that final spot or two with players like Joe Scally and Miles Robinson seemingly right on that fringe, and it seems that there may only be room for one of those two in the USMNT squad.
The midfield, meanwhile, is much busier. Outside of Adams, McKennie, and Tessmann, everyone else in those deeper roles is in a competition. That means that Pochettino will be choosing between the likes of Sebastian Berhalter, Johnny Cardoso, Aidan Morris, and Cristian Roldan, while Jack McGlynn could be looped into either this group or the more attacking group.
With the attackers, Pochettino will likely only be able to bring in two of Brenden Aaronson, Diego Luna, Gio Reyna, and Alejandro Zendejas. That choice may or may not be made on form, and if it is, then Reyna is quite clearly the odd man out. However, the fact that he was in camp on March proves that he may be a player worth making an exception for, which is why he remains on this bubble.