Marx new to base his analysis in real material conditions, but he was an idealist in his own way.
The state can't wither away, it must exist in an appropriate form of power, existing to restrain inappropriate bourgeois power. Men like Donald Trump will always come along with their elite bourgeois perversions of state power. They must be restrained.
If the state withers away, evil fills the vacuum. This is what happened in America. The state withered away by discarding its social function, transmuting itself into an arm of rich and powerful business interests shrinking to an elite core. Now evil fills the vacuum. The state is a tool of class rule, but it is also an essential protector against anarchy and individual predation. Angry people forget this, and only see one side of the coin. The very abuses of power that Marx sought to eliminate demands an enduring, organized political power.