1. Foreign entities are also investing in land that is strategically or tactically important -- agricultural land is a good example of the former; land near military bases an example of the latter. China has demonstrated a willingness to do both.

2. I think this represents a misunderstanding of the U.S. Constitution and U.S. law. The Constitution provides no power for the federal government to acquire land without just compensation, which courts have regularly held to mean fair market value. Put another way: The feds can likely devise a path for buying your land, but can't outright nationalize it. Changing that is not a matter of presidential decree or even a law by Congress; it would require an amendment to the Constitution itself, which is an extraordinarily heavy political and policy lift.