Beginning of the season through April 19: Cubs were hitting .319 with RISP (126 wRC+), which was good for 4th best in the MLB. No surprise, they went 11-6 over that stretch.
From April 20 through today: Cubs are hitting .214 with RISP (65 wRC+), which is second worst in the MLB. Unsurprisingly, they have gone 6-12 over that stretch.
Lots of different players to be blamed over this stretch. Really, all of them have essentially played a role at some point.