Depends on the type of ruling. The executive can't make the courts convict people willy nilly. The executive can't make the courts rule in civil cases the way he wants them to.
But mandamus orders against the executive really can't be enforced by the courts, not even the writ of Habeas Corpus -- and famously so, I might add, since Lincoln suspended the writ even though the Constitution says only Congress can do it, and he refused to bring people accused of sabotage or insurrection to the courts.
But mandamus orders against the executive really can't be enforced by the courts, not even the writ of Habeas Corpus -- and famously so, I might add, since Lincoln suspended the writ even though the Constitution says only Congress can do it, and he refused to bring people accused of sabotage or insurrection to the courts.