How did the failure at Malta by fdr and Churchill to adequately account for Stalin’s ambitions play into the final end of the war. Did it lengthen it or shorten it?
I wouldn't call it a failure on FDR or Churchill, it was basically at the time the Axis forces had Malta in a bottleneck. Being positioned in the Mediterranean Sea, that island was surrounded by the Axis. The sheer fact that Britain was able keep control of it (or what was left of it) throughout the war is no small feat. If anything Hitler and Stalin underestimated the resolve of the British to keep control of that island. In hindsight Stalin should have made Hitler make the island a priority instead of having Rommel pull forces away in 1941 when they almost had the island.
The fact that Malta was held by the Allies paved the way to destroy supply lines to North Africa and force Rommel to pull back to shorten the supply lines, giving Allied forces area to seize control and push Axis forces further back.