Yes, I believe that cyber attacks pose a serious threat to the United States of America. There are a myriad of people who don't fully understand the dependence of governments and countries on online tools and services, and these are the same people that downplay the seriousness of cyber attacks. In reality, cyber attacks could cripple entire nations in the matter of minutes, and they should be taken very seriously.
If you consider that everything is becoming digital and moving online, yest it will be a terrible threat. A cyber attack could bring down the electrical grid, the banking system, and a whole lot of functionality the government and private businesses need to use on a day to day basis.
Military operations, government secrets, even data from big business can be compromised from cyberattacks, which are ever increasing and endlessly bombard a target until one finds its way through and to what it is searching for. While there are many more immediate threats, successful cyberattacks can be extremely damaging and can compromise the safety of millions.
The attacks on our servers are increasing and this includes both government and private companies. The worry about these attacks is not only the loss of information about government and military movements, but also that corporate patents are under attack. Over the years China has show no interest in protecting copyrighted or protected information, and what they can glean from companies they can use to make fake competing products.