It all depends on his draw, just like all players outside the top 4. I don't know what his ranking will be for the US Open draw, but he should have some easy rounds to start off with. He could have the bad luck of drawing one of the big three after that, or a dangerous outsider as Ferrer, Blake, Gonzalez, YOuzhny etc. I believe he can beat anyone outside the top 3 with his current form, especially on the US Open courts, which are a bit slower than Washington if I'm not mistaken. He needs to skip this week however. A player of the category above could of course also be the end of his aspirations if he has a bad day. Best situation would be an idiot in round 1, followed by a mediocre placed guy. He could also draw someone like Gasquet, Davy, Ferrer or Roddick who are all struggling at the moment and are ready to be beaten by a guy like Delpo (even though I reckon Ferrer as a bad match-up for him).
I think Davy (if he's in any form) will be a bad match up for him aswell. He'll be able to feed off his power and move him around by taking the ball early like he does to Berdych. ANd like Berdych he doesn't have the variety to take Davy out of his comfort zone.
Del Potro isn't a bad mover for his size but he's still a million miles away from the elite in the game.
He deserves a nice draw anyway. From the start of 07 he went out to Gonzalez (Oz - Runner up), Nadal (RG - champion), Federer (Wimbledon - champion) and Djokovic (US Open runner-up). The Ferrer in Australia this year. He wasn't fully fit at RG and Wimbledon this year so you can't really base much on that.