This trivial concern has legs because it's a proxy attack channeling much deeper issues: the general discontent about the failure to produce convincing evidence of the WMD arsenal. And, the media/dnc has already lined up the next phase for whenever this one calms down, and are no doubt working on at least one or two more to push into the forefront after that...
As I've noted a few times, fixating on defending the trivial concern of the day is an exercise in futility so long as the WMDs aren't presented/explained to the public, because until that happens the real issue cannot get addressed. Meanwhile, the media/dnc will be going through every word in speeches & documents with a fine-toothed comb, lining up the next attack.
The uranium claim controversy itself probably has a shelf life of at least another week, because it's been in the media rotation for 15 days now and it takes two to three weeks before one may legitimately assess the approval ratings impact. The media and the democrats will near certainly keep this one live until at least another cycle of polls following that two week mark. Depending on interim developments, they may continue to push this avenue or switch to another - the 45 minute claim appears due next, although I've identified at least a half dozen statements open to attack.
Moreover, it's important to keep in mind that the DNC will want to time the major broadsides for this autumn and next spring, so the key objective of this interim buildup is simply to undermine GWB's trust factor. The timing of the Iraq report due some five or six months from now will be critical, depending on whatever that reveals. Assuming that it's perceived as a vindication of Bush, then this will simply serve to undermine his standing so as to minimize whatever bounce. Assuming it's perceived as a further indictment of Bush, then this will simply serve as a prelude to the subsequent controversy.
Whatever the case, the intention is to kneecap the administration long enough so that the economy may once again take the forefront. This isn't meant to bury Bush, but rather to negate any benefit from the Iraq campaign and/or the overall War on Terror. So long as the administration is encumbered with this issue, it undermines their ability to leverage other major issues/policies into the forefront. Note by example the general dismissal with which a drumbeat of statements regarding Iran & Syria have been met, since the administration cannot advance a credible policy in the context of these Iraq questions.
It also creates an emphasis shift from the positive aspects of the Iraq reconstruction to the negative. If the justification for war were impervious to dispute, then the emphasis would remain on the ultimate outcome. So long as the very rationale for our being there is questioned, then the emphasis shifts toward the interim difficulties. Much will depend on whatever the ultimate consensus appears regarding the whole WMD justification, as well as the progress made toward stabilizing Iraq overall. Again, this is primarily designed to submerge as much as possible any positive Iraq-related coverage, by tying up media with negative controversy.