I have a brilliant idea for keeping immigrants out of the United States. After all, why should our borders be open to people who want to steal our jobs, eat our children, marry our cattle, and become our leaders? This country was founded by old white men and I intend to help in any way that I can to keep it run by old white men. It is my dream that one day the United States of America will only be occupied by old white men. Living a completely heterosexual lifestyle of course.
So, here is the idea: The United States should physically remove itself from the borders of Canada, Mexico, Japan, Africa, and whatever other countries it may be touching. But this separation of land is not enough, the US is too good for Earth. Once the land has been separated The United State of America will be rocket launched into outer space where it can either float freely or attach itself to the Moon, Mars, or Arrakis.
Once The United States has completed its separation it will be impossible for those dirty immigrants to enter. Lasers will of course be used to shoot anyone that attempts entry, and a force field far superior to that of the Starship Enterprise will be devised. The United States will still, of course, have access to the abundance of resources on Earth, the endless supply of animals, water, plant life, and human slaves.
Separation is also great for when Earth finally collapses as a result of global warming, assuming that that is true anyway, but the US will be far away from the supposed destruction that awaits the planet and will continue to prosper.
It will be much easier to dictate from outer space. Enemy attack on our land will be impossible, but our weapons will reach any country that dares defy us. And if we should deem it necessary to drop a nuclear bomb on anyone or several countries, no harm will reach us.
The second phase of the plan will soon be implemented, in which all people of non-US blood will be deported. They can either return to their lands of origin or will be forcibly removed to Guantanamo Bay prison. What this program will do, The Alien Removal Program, is allow for pure US blood to flow freely and not become corrupted by any tainted non-US blood.
So, this is the basic plan. It needs some refining around the edges, but overall, I think it is good. And it can be achieved.