Possible but unlikely. The main reason why SOPA and PIPA were not passed wasn't the protests and website shutdowns, but the fact that Russia and China made it firm that cutting their websites from the Internet would be viewed as the same thing as a naval blockade... an act of war. With Congress afraid of their own shadow, it is no wonder why they backed down, saying it was the will of the people.
No way the entire Internet will be shut down by the US. First thing that will happen is that the UN would get handed ICANN's responsibilities, and the Internet would be up... but under new management.
Second thing is that no US Congressperson would allow it to happen. They get too much money directly from foreign donors, or indirectly companies made rich by foreign trade, which would be shut down in a trade war almost immediately.
I can see SIPRNet or NIPRNet having a master switch that shuts all core nodes of those down, but the Internet? Extremely unlikely. There is just too much big money that relies on the Internet, and if they can afford billions of dollars of computers for HFT, they can afford to get a President impeached who might even think of harming their business model.