Jannik's Road Back to #1

As a fan relatively new to following the sport, can anyone break down exactly what Jannik's path to #1 is? Yes, win tournaments, I get that. As I understand, he won so much last year that he has lots of points to defend, and if he's not winning he stands to lose them. But mathematically is it possible for him to regain #1 by end of year? And if so, how likely is it?