#4 United States Champion - Rusev
Rusev became the United States Champion on the very last episode of SmackDown Live 2018 when he defeated Shinsuke Nakamura. Also, the two men were continuously involved in a feud on and off. This title victory for Rusev came after a very long time.
That being said, Rusev is scheduled to defend his U.S Title for the first time since winning it. His first scheduled opponent is the former champion, Shinsuke Nakamura.
However, I think the chances of Nakamura regaining the title again are slim because if he is about to become the champion for the second time, he wouldn't have lost it to Rusev in the first place.
Moreover, I think the title is better off Nakamura as his reign as the U.S Champion is hard to remember. Therefore, expect Rusev Day to retain his title at Rumble against Nakamura.