Final answer:
The standard that established today's legal standard in the application of deadly force is objective reasonableness.
Step-by-step explanation:
The standard that established today's legal standard in the application of deadly force is objective reasonableness. This standard was developed through legal cases and precedents over time. One important case that contributed to this standard is Terry v. Ohio where the Supreme Court ruled that police officers can stop a person if they have a reasonable suspicion of a crime and frisk them if they have a reasonable suspicion that the person is armed and dangerous. Another case that shaped this standard is United States v. Miller, which upheld the government's ability to limit access to weapons that are not necessary for a well-regulated militia.