It's still early, of course - eight rounds remain - but it's so far, so good for 18-year-old Jeffery Xiong, who is having a spectacular March. First, he won the Spring Chess Classic in St. Louis with 6/9, ahead of superstars like Vassily Ivanchuk and Le Quang Liem, and now he leads the U.S. Championship with 2.5/3. He has gained 23 rating points this month, and is within 14 points of becoming the 6th U.S. player over 2700. His win in round 1 was already covered in the relevant post, and after a slightly hiccupy draw with Varuzhan Akobian in round 2 he won a crazy game against Sam Shankland in round 3 to regain the clear lead.
Three players are half a point behind: Wesley So, Hikaru Nakamura, and Leinier Dominguez Perez. So ground out an endgame win against Timur Gareyev in round 2, Nakamura won a heavy piece ending against Sam Sevian in round 3, and Dominguez won a rook ending with an extra pawn against Ray Robson, also in round 3. That almost exhausts the wins so far, but there was also an endgame win by Sevian in round two against Awonder Liang.
The games from rounds 2 and 3 can be replayed here; I've offered some notes to Xiong's games. Finally, here are the round 4 pairings: