North Korea announced its nuclear breakout in early 2003, kicking out international nuclear inspectors and very publicly beginning its drive to turn its stockpiles of spent nuclear fuel rods into a small arsenal of weapons. Focused then on the coming war with Iraq, Bush and his administration chose to set no limits.

But foreign policy, as Nunn says, is "all about priorities," and until Monday the closest Bush came to drawing a red line for the North was in May 2003, when he declared that the United States and South Korea "will not tolerate nuclear weapons in North Korea."

The Central Intelligence Agency's estimates in the years since have been that the United States has been tolerating exactly that — a small arsenal of nuclear fuel sufficient to produce six or more weapons.

Notably, Bush did not repeat that threat on Monday morning. Instead, he drew a new red line, one that appeared to tacitly acknowledge the North's possession of weapons. The United States would regard as a "grave threat," he said, any transfer by North Korea of nuclear material to other countries or terrorist groups, and would hold Kim's government "fully accountable for the consequences of such actions."

To critics of Bush's counterproliferation policy, this seemed a tacit recognition that the North had successfully defied American, Chinese and Japanese warnings about building weapons and testing them, and was now simply trying to manage the aftermath. If that is North Korea's strategy, it can learn from Pakistan, which exploded its first nuclear device in 1998, endured three years of sanctions, and is now considered a "major non-NATO ally."

Bush's aides say that if Kim believes he, too, can expect the world to impose a few sanctions and then lose interest in the issue, he is wrong. "He is really going to rue the day he made this decision," Christopher R. Hill, the assistant secretary of state for East Asian and Pacific affairs, said of Kim on Monday. But Bush's critics charge that the threat may be empty. As they see it, Kim watched the Iraq war and drew a simple lesson: That broken countries armed with nuclear weapons don't get invaded, and don't have to worry about regime change.

"Think about the consequences of having declared something 'intolerable' and, last week, 'unacceptable,' and then having North Korea defy the world's sole superpower and the Chinese and the Japanese," said Graham Allison, the Harvard professor who has studied nuclear showdowns since the Cuban missile crisis. "What does that communicate to Iran, and then the rest of the world? Is it possible to communicate to Kim credibly that if he sells a bomb to Osama bin Laden, that's it?"