But of course we are not doing that.
It should go without saying.
The U.S. annexed Puerto Rico in 1898, and it has been a U.S. territory ever since.
If the U.S. got involved in matters concerning Kaliningrad, or Siberia, then the authir would have a point. But Ukraine is an independent, sovereign nation that is a U.S. and whose sovereignty and territorial integrity was guaranteed by the U.S., the UK and Russia in a treaty. If the author wanted to use a proper analogy, he should have said that tbe U.S. becoming involved in the situation in Ukraine would be like Russia becoming involved if the U.S. took Vancouver Island from Canada.