A recent Bill Moyers program on PBS played audio tapes of Johnson on which he could be heard telling Defense Secretary Robert McNamara, “Not a damn human thinks that 50,000 or 100,000 or 150,000 [American troops] are going to end that war.”

McNamara replies, “That’s right.”

Nothing like those sentiments were conveyed to the public as Johnson and McNamara jacked up the draft and started feeding young American boys and men into the Vietnam meat grinder.

Afghanistan is not Vietnam. There was every reason for American forces to invade Afghanistan in the immediate aftermath of Sept. 11, 2001. But that war was botched and lost by the Bush crowd, and Barack Obama does not have a magic wand now to make it all better.

The word is that Mr. Obama will tell the public Tuesday that he is sending another 30,000 or so troops to Afghanistan. And while it is reported that he has some strategy in mind for eventually turning the fight over to the ragtag and less-than-energetic Afghan military, it’s clear that U.S. forces will be engaged for years to come, perhaps many years.

The tougher choice for the president would have been to tell the public that the U.S. is a nation faced with terrible troubles here at home and that it is time to begin winding down a war that veered wildly off track years ago. But that would have taken great political courage. It would have left Mr. Obama vulnerable to the charge of being weak, of cutting and running, of betraying the troops who have already served. The Republicans would have a field day with that scenario.

Lyndon Johnson is heard on the tapes telling Senator Richard Russell, chairman of the Armed Services Committee, about a comment made by a Texas rancher in the days leading up to the buildup in Vietnam. The rancher had told Johnson that the public would forgive the president “for everything except being weak.”

Russell said: “Well, there’s a lot in that. There’s a whole lot in that.”

We still haven’t learned to recognize real strength, which is why it so often seems that the easier choice for a president is to keep the troops marching off to war.