It's a high priority of Bush's, and he is running against two quickly ticking clocks.

One is his own. His presidency is set to end in a mere seven months.

The other is Iran's. In defiance of the first three rounds of mostly symbolic UN Security Council resolutions, Tehran has not only continued its enrichment of uranium, producing material that could be used to power an electricity plant or make a nuclear bomb, but also has expanded and improved it. Assessments vary widely, but it is widely presumed Tehran will have enough fissile material for a weapon within a few years.

A US intelligence report in December said Iran once had an active warhead program, but shelved it in 2003. But the administration believes that's nowhere near the last word on Tehran's desire for a nuclear weapon. It argues that the continuing enrichment means the military program could be restarted at any time, and without the knowledge of the outside world.

Those competing to succeed Bush, Democrat Barack Obama and Republican John McCain, have differences over whether to talk to Iran's leaders. But both have pledged to be as tough as Bush – including holding out the threat of force – to prevent Iran from becoming nuclear-armed.

Still, either administration will take some time after the January inauguration to gear up, both in personnel and policy development. And that is time that Bush and his administration fear cannot afford to be wasted.

"It's just this sense of how much time can, in a sense, be lost before the Iranians do something very significant?" Flanagan said.

So the president is on a tour of persuasion.

"I will continue to work on this trip to talk about the dangers of a nuclear Iran – not civilian nuclear power, but a program that would be aimed at blackmail or destruction – and that we've got to work to stop them from learning how to enrich," Bush said in an interview with RAI TV of Italy.