The 4,000 US troops that arrived in Poland today are part of a massive expansion of NATO eastward to Russia's borders that began long before the situations in Ukraine and Crimea being used to justify it.
Those situations, whatever you think of Vladmir Putin, were Russian reactions to US aggression. In Ukraine, the US engineered a coup in 2014 that ousted an elected government that opposed Ukraine joining NATO, after which the US installed a government it can bend to its imperialistic needs.
Crimea, annexed by Russia after Crimeans voted to leave Ukraine, was formerly part of Russia and is still inhabited largely by Russians. After the 2014 coup fascist mobs with the acquiescence of the new coup government began to threaten and in some instances attack Russian Crimeans, leading to the vote of succession after which Crimea again became part of Russia. Crimea also houses a Russian naval base, one of only two small warm water ports it has, i.e., that are accessible during winter.
The fact that two of the parties behind the Ukraine coup and now in the quisling government are fascist was not a concern
of the United States government and the Neocon dominated "deep state"
foreign policy establishment that includes parts of the military and
intelligence communities and which exerts domineering influence over US foreign policy and is the force behind the still expanding new Cold War
the US has launched against nuclear armed Russia.
Poland is one of many European nations where governments with extreme right wing agendas, sometimes with fascist leanings, recently have come to power, largely because of what is commonly called the "refugee crises," a mass exodus of refugees from the many ongoing US wars of aggression in the Middle East and North Africa.
This map from a masters thesis also shows NATO expansion. The numbered states were NATO members before the dissolution of the Soviet Union. The lettered states are former Soviet states that have joined NATO since then. The black line shows the former demarcation between NATO and the USSR.