He didn't "taking the US off of it". He confiscated the gold of American citizens, and did so by executive order. US dollars continued to be exchangeable for Gold -- to foreign central banks. NIXON, ended that, not FDR.
FDR appeased Stalin and allowed him to seize Eastern Europe. Just as Neville Chamberlain thought it was OK for Hitler to seize Poland, so too did FDR think it was OK for Stalin to seize it. Poland was not FDR's to give away. Nor were any of the other nations.
The Polish Free Army fought Hitler until Warsaw was reduced to utter rubble, then they fought the Soviets. The Poles were not incidental to WW2, they were allies of the first order.
And they were betrayed by FDR.
In Poland, and many of the other "captive nations" you will find statues of Ronald Reagan for a reason. There are no statues of FDR.
It is difficult to "sweep too broadly" in condemnation of FDR, he was a fascist loving creep who did more to set us on our present course than any other single individual.
May he rot in hell.
Just how did FDR allow Stalin to seize Poland? The Soviets occupied Poland as a consequence of defeating the Nazis. The issue was whether after the war, Stalin would permit the Poles to have free elections and form a government of their own choosing.
On that issue, the West had little leverage. There is some reason to think that after Yalta, FDR had at last begun to realize that Stalin had lied and could not be trusted, but FDR died before he could take action and it was his successor Truman -- yes, Truman -- who negotiated a deal with Stalin after WW II that effectively abandoned the pro-Western Polish exile government in London. It is not clear though that a better result could have been obtained by diplomatic means.
Of Polish extraction, I am acutely aware that Poland's fidelity to the Allied cause in WW II was exemplary yet, in a world little given to fairness and justice, Poland suffered terribly during and after WW II. This included my Polish grandparents' ancestral home region, which was looted and had its Jewish population murdered by the Nazis, and then, after WW II, was looted again and burned to the ground by an invading army of Ukrainian partisans led by an SS colonel.
Might the US under FDR and Truman have rescued Poland from the cruelties imposed by bad neighbors and unfortunate geography? Immediately after WW II, weary Americans were not willing to go to war with the USSR for the sake of liberating Poland and Eastern Europe. And once the Soviet nuclear program tested an atomic bomb in August of 1949, any direct fight with the Soviets had to be avoided because it would have involved the existential menace of nuclear weapons.
As it was, in the 1980s, with Reagan as President, the US helped Poland to liberate itself from communist rule and set in motion the events that destroyed the Warsaw Pact and fatally discredited Communism and the Soviet Union. I suspect that more than once curses were whispered in the Kremlin against Stalin for thinking that Russians could indefinitely rule over the Poles.