Let's say some group joins together in America and want to oppose the government and they send their messages by terrorizing U.S events? What would the U.S do to take these actions?
The UK had to endure many years of that kind of thing from the IRA (who were partly funded by the USA). All litter bins (trash cans) were removed from train and bus stations and other public places. CCTV cameras were put up everywhere.
People become more diligent, any bag left unattended anywhere would be reported immediately.. Suspicious cars would be blown up by the security forces. Generally, life changed for everyone. Eventually you get used to it. Every now and then a bomb would go off, people get killed and injured. It becomes the way of life and you have to adjust to it.