JEFFREY BROWN: Also this weekend, and again today, the Bush administration asserted it was not looking to provoke a war with Iran.

And for more on all of this, we get two views. Flynt Leverett covered Middle East terrorism and political issues at the CIA, State Department, and on the National Security Council staff from 1992 to 2003. He's now a senior fellow at the New America Foundation...

Mr. Leverett, what is your overall reaction to yesterday's briefing?

FLYNT LEVERETT, The New America Foundation: First of all, I don't know that the forensic evidence was particularly strong.

But even assuming that at least some of the evidence that was put on the table demonstrates that these weapons were manufactured in Iran, and that in at least some cases they were of relatively recent manufacture, it's a little bit like saying that you're shocked to learn that there's gambling going on in the casino.

Iran fought an eight-year war with Iraq. It had, before the U.S. invasion, a 20-year record of providing support, including military training and equipment, to Iraqi opposition groups, including Shia militia groups allied to major political factions in today's Iraqi political life.

In the post-Saddam period, it should not surprise us that Iran has worked hard to maintain very active ties politically, militarily, in other ways with all of the major actors in Shia politics.

This is not something new. This is not something that I think is particularly surprising. The real questions are: How significant is it? And what should the policy response be?

JEFFREY BROWN: You think the timing here and the way this was done -- there was a lot of attention to how this briefing was done yesterday -- that was fishy a little bit, in terms of what they were trying to put out there?

FLYNT LEVERETT: I think that there is something not coincidental about the timing of this. Basically, the administration is focusing attention on Iran's role in Iraq right now because its own policy is failing...

For the complete transcript, please visit the PBS website.