If the info came from the Bush administration, then I'd say it was because some of our allies, notably Pakistan, may be starting to have cold feet. Or maybe it's time to start the coalition building that will be needed for a strike on Iraq and proof of Iraq's involvement in this terrorism will help a lot toward that aim.
But it may not have come from Bush. It could have come from people affiliated with Daschle or Daschle himself. I'm sure he's being kept up to date on all the developments and it would be awfully hard to keep this one quiet.
Several things may be involved here. One, the charade played by Israel and the US the last few weeks is beginning to be untenable. You can run a smoke-and-mirrors game only for a limited time before people get suspicious. Two, there may be hard evidence that Pakistan's nukes are not actually under firm and sensible control. Three, the rumours about bin Laden being dead may actually be true and the Afghan bit done except for the mopping-up.
So, time to move to the next target in line.