"Who was worse: Hitler or Stalin?"  It isn't a parlor game, but rather the historical equivalent of "ISIS or Iran (or proxy Syria)?"  You can play it either way, but "a plague on both their houses" didn't cut it in 1941, and it doesn't cut it in 2015. 

The Molotov-Ribbentrop Pact of 1939 gave Hitler room to conquer Western Europe without fear of an attack on his rear.  Stalin was a committed member of the pact until Hitler broke it, at which point Stalin brazenly pivoted to the Allies and demanded rights as a) a full partner and b) an aid recipient.  FDR might have said, "Boy, watching Adolph and Uncle Joe battle it out would be great – fascists vs. communists, and no American boots on the ground."  But even before Pearl Harbor and Germany's declaration of war against the U.S., FDR and Churchill set aside their disgust for Soviet internal behavior.  They knew full well about the millions dead in the Stalin-engineered Ukrainian famine, even if Walter Duranty was keeping it from NYT readers.  But they determined that Hitler was the greater immediate threat.  

FDR made a great many difficult and ugly decisions – aside from interning Japanese-American citizens and not bombing the railroad tracks to Auschwitz. In this context, he made two for what he thought was the greater good: ignoring Stalin's crimes, and committing all the resources necessary to achieve the unconditional surrender of Axis forces.  He put the American economy on a war footing, drafted millions of soldiers, and dropped tons of bombs that often didn't distinguish between military forces and civilians.  He believed that the faster the war ended, the better it was for the civilians and everyone else.  It wasn't a perfect understanding – particularly for the Jews waiting for deliverance.  But it was his understanding, and Truman concurred. Dropping the atomic bomb on Hiroshima and Nagasaki was a calculated decision to take the casualties, including civilians, up front.

It is also worth remembering that the Allies never did turn their armies toward Stalin – to the dismay of millions of prisoners of the gulags, millions more forcibly detained in the Soviet empire for the next 45 years, and captive Soviet Jews.  But the Allies – meaning America – did in fact create the framework for 70 years of multilateral understanding in Europe and Asia.  The Cold War was the diplomatic way of boxing in the USSR until it collapsed.

That is not a tactical proposal for coming to grips with the dual horrors of ISIS and Iran.  It is a strategic one. 

The United States, President Obama, has to decide who the primary enemy is and how best to stop that one.  Vladimir Putin posits that ISIS comes first, and requests – begs – the West to take on Sunni jihadists while giving Shiite jihadists a pass.  He makes a decent case for the immediacy of the threat of ISIS to the region and beyond.  Iraq – our putative ally – joined Iran and Syria last week in approving the Russian position.  France joined this week by bombing an ISIS training camp in northern Syria in what it called its first strike.  China claims to be in Russia's coalition as well.

It is untenable for the U.S. to continue to dither.  It is difficult to imagine a less productive activity than reminding Americans, as the president did in a town hall meeting two weeks ago, "I told [Putin] it was a mistake … he did not take my warnings. ... You can't continue to double down on a strategy that is doomed to failure."

Spending half a billion dollars training small groups of Syrians who lie when they pledge to fight ISIS rather than Assad; failing to provide weapons to the Kurds, who constitute the only serious fighting force south of Turkey; doctoring CENTCOM intelligence; and hectoring Putin – as the president did and continues to do – are also doomed to failure.

The grinding fighting across Syria expands the void that ISIS and similar groups enter by osmosis.  Regional chaos also empowers Iran, arming and funding both Sunni and Shiite groups committed to destruction of the West and Israel.  A long-term, low-level conflict will further the collapse of modernity in the Arab Middle East, exacerbate the refugee crisis, and move the problem to Europe through flows of refugees laced with ISIS operatives.

The U.S. no longer has to see the world primarily through the prism of petroleum interests.  Forty-plus years after the first "oil shock," we are rediscovering our own resource base.  We tried substituting "democracy promotion" as a slogan to justify American intervention in the Middle East and North Africa – it wasn't true, and it didn't work.  But the notion of the "free world" should still animate American political and economic interests.  Progress is made through the free exchange of goods and ideas, and people of the Middle East and other vulnerable parts of the world should not be cut off from that progress.

Thomas Hobbes is the prophet.  "Where there is no common power, there is no law, where no law, no injustice. Force, and fraud, are in war the cardinal virtues. No arts, no letters, no society, and which is worst of all, continual fear, and danger of violent death: and the life of man, solitary, poor, nasty, brutish and short."

If that works for you, fine.  Otherwise, it is time to choose and get on with the war that is already raging around us.