From Lebanon to Iraq to Kosovo to Iraq (again) to Afghanistan, they all went to the people to argue that the threat or the use of limited military power might be necessary in the pursuit of national security and a safer world. But Americans have learned in the last two decades that threats of military action have usually turned into genuine military action.

Gerald Seib write in The Wall Street Journal:

Tyrants and terrorists eventually will threaten the U.S. if weapons of mass destruction flow unchecked across the international landscape.

And ultimately, he made the argument that the plausible threat of military action makes it less likely that action will ever actually occur.

The specter of a military strike already has, in the last two days, prompted a diplomatic flurry in which Syria has acknowledged it has chemical weapons, and agreed in theory to surrender them, Mr. Obama argued. Only a continued military threat will keep that slim diplomatic hope alive.

On its face, that case isn't much different from the one that his recent predecessors, from Ronald Reagan through George W. Bush, all found themselves making at one time or another.

From Lebanon to Iraq to Kosovo to Iraq (again) to Afghanistan, they all went to the people to argue that the threat or the use of limited military power might be necessary in the pursuit of national security and a safer world.

But the ground now has shifted. For starters, Americans have learned in the last two decades that threats of military action have usually turned into genuine military action.

Moreover, the president now saying military action in Syria might be in the nation's interest has, in fact, spent the last two years arguing that intervention in Syria isn't in America's national interest.

So Mr. Obama asked Americans to agree with him that the use of chemical weapons had fundamentally changed that equation.

More than that, though, he insisted a military response to those chemical weapons would emphatically not be a repeat of Iraq and Afghanistan, which turned into prolonged ground wars, or even of Libya, where an extended air campaign was needed to throw out the regime of Moammar Gadhafi.

The problem is that he is speaking to a country where many have heard such promises of limited military action before, and don't really believe that is the way these kinds of dramas end.