The government is rightly concerned about terrorism, specifically CBRNE forms of terrorism. CBRNE stands for Chemical, Biological, Radiological, Nuclear, and Explosives...in other words, methods that are unexpected yet pretty much guaranteed to take out a lot of people and cause, well, terror.
While these forms of terrorism are always possibilities, they haven't been top of mind for me for over a decade. Until last night. The news came on in the afternoon about the police dealing with a hazmat situation which required the neighbors in the area to shelter in place. Most hazmat situations are resolved within a few hours. When this situation was still ongoing 12 hours later I figured "hazmat" was more like "ebola" or something equally not good. Turns out the problem was ricin which is, well, not good either.
CBRNE forms of terrorism have been used with varying degrees of "success" over the years. The sarin gas attack in Japan killed 12 people (chemical), the Rajneeshee food poisoning attack back in the 1980s sickened 750 people (biological), Alexander Litvinenko was poisoned with polonium a decade ago and "dirty bombs" are always a concern (radiological), fortunately nuclear attacks remain a possibility but haven't been used in terror attacks--yet--and there have been numerous examples of explosives used for terror purposes including the Oklahoma City bombing and the Boston Marathon bombing.
These sorts of attacks are sudden and unexpected and can happen quickly such as a bombing incident or a gas attack when people immediately start dropping or they can take place yet people won't know they have been attacked until later like in the case of Litvinenko feeling ill and it taking a while to figure out how he had been poisoned and what he had been poisoned with.
Needless to say, the government is concerned about such attacks taking place because they can be hard to preempt, in some circumstances hard to detect immediately, and have the possibility of injuring and killing a lot of people. In addition, wide-spread terror impacts not only the people immediately involved but everyone in psychological, financial, and security terms.
Preparedness for CBRNE attacks mostly rests with the government. The government works with a variety of agencies (law enforcement, hospitals, etc) to fund programs for everything from radiological monitoring at large public events to syndromic surveillance programs for early detection of health indicators to training and preparedness for large scale disaster events.
As an individual, there is not a whole lot you can do to prevent such incidents except for being aware of your surroundings, reporting anything out of the ordinary so law enforcement can check it out, and using common sense (if you see someone "forgot" their Instapot in a public area don't pick it up--report it immediately and get away from it!). If you think you have been a victim of CBRNE terrorism (you are in an urban environment and a low flying plane sprays the area with chemicals, you are at a public event and become violently ill, etc), isolate yourself (in your vehicle, don't bring the contamination home to your family or walk into a hospital and possibly contaminate everyone there), then call 911 for instructions on what to do (they may send you to a decontamination location or send EMS to assist you). Finally, take photos and videos of suspicious people/things/events and take notes about unusual things (license plate number, time order of events, etc) to give to police to use in their investigation.