Is isolationism a feasible policy in today's world?
For the United States, isolationism is probably not a feasible policy today. The reason for this is that our economic health is tied so closely to the overall world economy. Because of this, it is important for us to maintain a world order that allows for free trade.
To take one example, if Iran were to go through with its threat to close the Strait of Hormuz, there would be serious consequences for the world economy. If the world economy were to enter a downturn because of a decrease in the supply of oil, that would harm the US economy a great deal. The same sort of problem would likely arise if the US allowed pirates operating out of Somalia to shut off shipping in that area.
Because so many things that happen in the world have an impact on the US economy, isolationism seems not to be feasible.