Why S-400 couldn’t defend itself from ATACMS fired from HIMARS

at first a lot of (good ) technical detail of capabilities ......but if you want to skip to the chase - start at 7 min30
in short .....the S-400 SHOULD'VE been protected by short range systems ...presumably wasn't .....not the first time either
net result - a very expensive system doing an important job demised rather cheaply and easily