The official word from the White House on how worried to be at this point:
Reporter: "Is there still a situation of concern, as opposed to alarm?"
White House spokesman Robert Gibbs: "I think so. I mean, I think the way — I would phrase it the way the president did: It's a very serious situation and one that requires serious precautions. I think that's what he outlined today. I think that continues to be his concern and he continues to ask questions of those that are involved in this to ensure that we're taking every step and precaution that's possible to ensure safety."
(From the official transcript of Gibbs' "gaggle" with reporters aboard Air Force One this morning as the president flew to St. Louis.)