"With Russian forces entering into Ukraine, NATO is putting together a plan to place the alliance's troops in bases behind the former Iron Curtain. One U.S. official who was not authorized to speak to the press said the presence of U.S. troops inside these bases in Poland, Romania, Lithuania, Latvia, and Estonia would act as a "tripwire for Russia. If Putin considers any military action in these countries, they will know that they will be involving U.S. forces too."