The US Government really wasn't in a position to do much to aid Poland in 1939. Our military was not that strong in 1939, and there was significant public resistance to entering the war. An expanding Germany was a clear threat to the UK, so their elected officials had no trouble convincing their public that war was necessary. In the US, it was less clear, and it wasn't until Pearl Harbor that the populace of the US was convinced that the Axis had to be stopped.

To answer the question of the government's desire to enter the war, they had at least two documented sources (one a British asset in Europe), another in Japan warning them that the Japanese were planning to attack Pearl Harbor, and giving an approximate date for that attack. The US government did nothing to warn Pearl, or prevent the attack, because it was the only way to get the US population to allow them to enter the war.



I have yet to see any indication that the American government agreed with the Molotov–Ribbentrop Pact. Indifferent maybe. But no agreeing. Many in the US saw the USSR as as big of a threat as the Nazis. The remainder wanted no part in a "European" squabble.

The US did not start sending aid to the USSR until the day the Operation Barbarossa started, the USSR found itself at war with Germany, and allied itself with the UK.