Poland is a member of NATO, as is the U.S.
Per Article 5 of the North Atlantic Treaty:
"It commits each member state to consider an armed attack against one member state, in Europe or North America, to be an armed attack against them all. Upon such attack, each member state is to assist by taking "such action as [the member state] deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."
Ukraine is not a NATO member, so there is no such obligation.
You are correct.
As for NATO, I have zero desire for the US to be in NATO. We rebuilt Europe after WWII, it is about time they stand on their own two feet and pay their way. While we are in NATO we have to abide by the treaty. With that said. It is time to exit NATO. Let them go cold turkey.