The point of checks and balances was to make sure no one branch would be able to control too much power, and it created a separation of powers. Here are some examples of how the different branches work together:
The legislative branch makes laws, but the President in the executive branch can veto those laws with a Presidential Veto.
The legislative branch makes laws, but the judicial branch can declare those laws unconstitutional.
Unlikely, but it could happen
The answer is police discretion, this is a type of decision which
is in particular with police officers of having to decide whether the matter is
ignored as it is part of their work or either to get someone arrested.
