Obama, better than anyone, also knows the rules of today's political opportunism. Currently, liberal hawks are calling for Syrian intervention on humanitarian grounds. They are echoed by many conservatives seeing intervention as a way of both hurting enemies such as Iran and Hezbollah while helping friends such as Arab reformers and Israel.
Yet put Americans on the ground in Syria, fighting both the Assad regime and al-Qaeda, with rising costs in blood and treasure at a time of near national insolvency, and yesterday's assorted zealots will quickly become today's "I told you so" critics.
Obama must remember the fiery 2002 speeches of then-Sens. Hillary Clinton, John Kerry and Harry Reid authorizing the Iraq War. He read the once-impassioned pro-war columns of New York Times and Washington Post columnists. So he also recalls that all such interventionist zealotry soon turned from "my brilliant three-week victory over Saddam" into "your botched multiyear occupation" once the Iraq insurgency took off, American costs skyrocketed, and national elections loomed.
Without a credible follow-up of using force, Obama's once-soaring warnings have become stale and no longer earn any deterrence. Even a Nobel Peace Prize laureate can only so many times thunder about "red lines" and "game changers."
After serial but inconsequential deadlines to cease their nuclear enrichment, the Iranians now snooze when lectured. Assad bets that the danger of American retaliation for crossing the WMD red line is far less than the danger of losing his rule -- and his life.
North Korea looks at the latest Obama remonstration to act responsibly in the same way most Americans regard his erstwhile promises to close Guantanamo within a year, or to dismantle the Bush-Cheney anti-terrorism protocols: mellifluous idealism not necessarily followed by unpleasant implementation.
China increasingly believes that the U.S. president is more interested in reducing our deployable nuclear warheads than in warning aggressive Red Army generals that Japan, South Korea and Taiwan are firmly protected under the American nuclear umbrella.
In the end, we are left only with hope for change. Maybe Iran and North Korea will come to their senses and behave. Maybe Assad will finally fall. Maybe the Syrian insurgents will prove to be pro-American democrats after all. And maybe opportunistic senators and journalists will not play politics and one day abandon the very policies that they once urged their president to adopt.
And then again, maybe not.