Well, in the idea of the system there is: The system is built around the assumption that Congress would impeach a president who fails to to the right™ thing (or fails to make his administration do ...)

However once the legislative branch surrenders oversight over executive there isn't much left keeping the system in balance. Even if judicial branch would call a measure unconstitutional, who'd execute that ruling?

The system is built around the assumption that a notable part of the system wants to keep it alive.