135 U.S. 1 (1890)
Facts of the Case: Suspecting a plot against Justice Stephen J. Field’s life, the U.S. Attorney General appointed Neagle, a U.S. Marshall, to protect him. Acting as Field’s bodyguard, Neagle shot and killed a man who appeared about to attack the justice. After California officials arrested and jailed Neagle, the U.S. sought his release by a writ of habeas corpus, wrongful conviction.
Issue: Was the state obligated to obey the writ even though no national statute empowered the Attorney General to provide judges with bodyguards?
Conclusion: Yes. The Court held that the Attorney General acted appropriately since assigning Neagle as Field’s bodyguard assured that the nation’s laws would be faithfully executed (President shall take care that the laws be faithfully executed).
Furthermore, Neagle’s actions were consistent with a congressional statute which provided U.S. Marshalls with “the same powers, in executing the laws” as state sheriffs and deputies (who would have been allowed to deter an attack on Field’s life).
There are some emergency powers, but the courts don’t just blatantly say the executive branch can do whatever they need at the time. The court must look to some form of statutory authority.