Tatum hasn't been able to sustain his hot start but I think his "slump" is being overblown.
In 6 games since the all star break, he's averaging only 10.7 ppg but shooting .451/.533/1.000 and turning it over less than once per game.
Since January 1st, he's averaging 12 ppg on .425/.375/.864.
He's playing fewer minutes, which is indicative of some of the problems he's had as the season has gone on but he's still giving the team productive minutes. I'm not worried. Especially, as others have said, things slow down a bit in the playoffs and there are no back-to-backs which should help him.