We have been at war for many decades with several adversarial nations and governments that wish us harm, and who are constantly assessing our strengths and weaknesses in various ways.
They test security at public buildings and facilities using social engineering techniques. They attempt to gain access to government computer systems. They conduct surveillance at government or military facilities or installations. They try to befriend, bribe, or compromise elected officials or others who perform security-sensitive jobs, or who have access to classified information.
Most Americans are blissfully unaware of this activity until it makes the news, but it goes on all the time, and there are thousands of US Government employees whose job it is to protect our country from these bad actors.