The best way to stop a person from entering the USA by visitor visa if he or she is a threat to one or more US citizens is to report the person to the Department of Homeland Security. They will need the person's full name, the nature of the threat, and where the person is likely to try to enter the US.
lan owners lol
watch your profantity
the government helps citizens by creating laws to help protect them from ANY threat including themselves
China's government sees the internet as a threat - because it suppresses its citizens by censorship. Certain websites are blocked by China - so their citizens cannot access them from within their country.
malaria
Demosthenes warned his fellow citizens of the looming threat from Philip II of Macedon because he believed that Philip's ambitions posed a serious danger to Athenian freedom and democracy. He urged his fellow citizens to unite and stand against this threat to protect their city-state's independence.
the government helps citizens by creating laws to help protect them from ANY threat including themselves
Ostracism was a procedure in use during the time of Athenian democracy. It gave citizens of Athens power to send in exile of up to ten years a person who was deemed to be a threat to the state or potential tyrant.
In the 1970's it was the threat from Cambodia, scaring many citizens to flee.
State governments
It decreased citizens rights
Because it could be a threat to citizens or even other countries when applied