Some states like California and Texas have had a vote to secede they had hundreds of thousands of supporters, the states with 20 delagates or more would be all right if they seceded, California, Texas, Florida, New York, Pensilvania, Illinois, but the delagates in congress would drop and the elections would be more random for the US, the secession would last at most 30 years because of economy and a presidential candidate for the white house would easily win if he told that he'll unite the US so then the states would have to survive the ambitions from the president. Secession would be a good idea, but if the states would want to remain they would have to think which road to take.
Look in the past of what the affect was when states seceded from the United States, Civil war. The states that seceded back then were self reliant and they could trade and its the fact of how the remaining states react we would have large arguments over what belonged to the remaining states and the states that seceded taxes in the remaining U.S. would have to pay much higher taxes due to the loss of people, more than likely another civil war would begin.
The civil war began because President Lincoln entered office, at that point the first confederate states seceded. The reason they couldn't trade was because the navy encircled their entire coast so ships couldn't leave. Due to current standards if those states seceded the Civil war would be a loss to the US, the entire population of the states that I chose would add up to more than 115 MILION people, not every one would fight in the war, but if they had a cause to fight, Many would stand to fight. The reason for secesion and their cause would be Terrorism or other Problems like national debt. But if they left the US would fall dramatically they would lose their most reliable states, america wouldn't die it would just fall in a worse crisis. A civil war reclaiming the other states would be pointless and would end up a failure for the US, if the other states would pay taxes then they would follow the steps of the seceded states, then america would fall. then a battleground would win ending up in the first seceded states gaining their own territory and satellites. The fall of america would shock the world, but the seceded states would probably ally them selves with NATO, or the Communist Allies, Farm states would mostly ally themselves with the Communists.