Condi Rice channels Churchill:
“When you threaten Poland, you perhaps forget that it is not 1988,” Rice said. “It’s 2008 and the United States has a … firm treaty guarantee to defend Poland’s territory as if it was the territory of the United States. So it’s probably not wise to throw these threats around.”
As Pat Buchanan has chronicled, the last time a great Western power decided to offer Poland a firm treaty guarantee against foreign attack, it ended up bankrupting itself and losing its status as a great power. Russia has survived being on the losing end of wars more than once before, so I suspect Putin is correctly calculating that he can afford to lose this one more than the USA can afford to win it.
So, the reality is that the USA isn’t likely to do anything even if Russia invades Poland. We can’t afford to, not without giving up on the goal of attacking Iran and neither side has any interest in going nuclear over it.