The chief issue of the day was whether to escalate the war further or de-escalate. There were economic concerns. And there was a president "too intent on a search for consensus," as historian Robert Dallek wrote in his biography of Lyndon Johnson.

It was early May 1966. The first time Johnson's public approval rating fell below 50 percent in the Gallup Poll. A month later, on June 9, Press Secretary Bill Moyers informed Johnson that, "Conversations with Gallup, Harris, and other professionals in the poll business confirm only one thing: Our standing is down and likely to drop further."

It will not, of course, take this president an entire month to digest the same bad news. And that bad news will likely come sooner for Barack Obama than most previous presidents.

If Obama falls below 50 percent before mid-November, it will mark the third-fastest rate since World War II.

Obama is on the edge. The new Gallup/USA Today poll has Obama's approval at 50 percent. He first saw 50 in the Gallup tracking poll in late August. He has since returned to that precipice on several occasions, as he did Wednesday, only to slightly recover.

The Afghan war now weighs down Obama. He too is a man who has long sought consensus. The defining trait of Obama now dogs him. In health care, progressives sense momentum on the public option. They want Obama to personally take up their fight.

Obama may soon choose sides. He recently took a firmer hand to Wall Street. He is talking in more partisan tones. He may still take up the public option on health care. A fall below 50 can spur those choices. It did for Johnson. But the middle way is also a choice.

Below 50, Johnson distanced himself from the most vulnerable Democratic congressmen. He wanted to appear less partisan. He went to the Midwest for big speeches. He met on background with reporters. And he bombed, escalating the campaign in North Vietnam. Johnson briefly recovered, only to soon fall again.

Johnson had his problems with inflation. Obama's has it far worse economically. And for this president, it will still get worse before it gets better. Unemployment will likely soon reach double digits.

The cause of the fall is not, at first, the news. It's the majority lost. Fifty percent means mandate. It's symbolic, not unlike the Dow Jones 10,000 mark. Insignificant but for what it captures. And in a republic, it captures power. Public approval is the currency of political capital. It's how platforms become policy.

Below 50, the framing of Obama's presidency will be altered. A majority lost, even once recovered, can be lost again. After a heavyweight champion is first knocked down, his opponent knows the champ can go down. It will be like that for Obama.

Political opponents will pounce. National stories will tell of a president who has lost the people. Even at 49, the president is in charge of the same divided nation. But the view has changed. Below 50, the bully pulpit loses its bully. Legislative battles become more difficult.

In the age of tracking polls, a president can fall below 50 and come back the next day. But once the fall is sustained, it sticks. And in this manic news environment, sustained means only a matter of days.

Gerald Ford (after three months) and Bill Clinton (after four months) were the first presidents to lose the majority. But unlike Clinton, Obama won with a majority. It's his to lose. So the loss would mean more.

Ronald Reagan and Harry Truman are the other two presidents to lose the majority during their first year. Reagan first fell below 50 in mid November 1981. It took Truman 11 months.

John F. Kennedy is the only modern president never to fall below 50. His approval rating was in the high 70s at this point in office.

Early on, Obama proved unable to emulate Kennedy's appeal. His problem is now more ordinary. Even excluding Kennedy, Obama's modern predecessors lost the majority on average after 23 months in office; the median was 13 months. Obama has served nine.

Nothing is written. Obama might hold the majority far longer. The bulk of his decline came over the summer, largely due to the health care debate. His polling has since stabilized. But the extent he has already fallen is striking.

On Wednesday, Gallup reminded Obama of what was lost. Obama had the worst third quarter decline in public approval of any elected president in the post-war era.

Still, it's the fall below 50 that hits hardest. Some presidents never do recover. Like Johnson, George W. Bush and Jimmy Carter could not.

But Reagan reminds us that a public can be won back. Reagan, like Obama, faced the worst recession to date. He languished for two years below 50 and went on to win an historic landslide.

Obama is his own man, in his own Washington. No analogy is perfect. But all successful presidents need the public at their back. And Obama remains a most ambitous president.