And the C.D.C.’s missteps have much different implications from the errors made by the Secret Service and by Veterans Affairs. Individual Americans don’t fear that the Secret Service’s lapses will endanger them personally, and many of them aren’t directly affected by the wrongdoing of hospitals for veterans. But they can imagine themselves on one of those flights or in some other closed space with an infected person. They feel vulnerable.

Because the Ebola response deepens doubt about the current government, it almost certainly hurts incumbents in the midterm elections and favors change. That’s unhappy news for Democrats as they fight to retain control of the Senate, and by the end of last week, they were spooked. I heard that not only in my conversations with party strategists but also in the statements of Democratic candidates themselves.

BRUCE BRALEY, locked in a tight Senate race in Iowa, publicly upbraided the Obama administration for what he characterized as a sluggish response. Al Franken, running for re-election in Minnesota, said there should at least be serious consideration of the sorts of flight restrictions that Obama has dismissed. Even Jay Carney, the president’s former spokesman, mentioned such restrictions as potentially wise policy.

Rationally or not, this is one of those rare moments when Americans who typically tune out so much of what leaders say are paying rapt attention, and Obama’s style of communication hasn’t risen fully to the occasion. Even as he canceled campaign appearances and created a position — Ebola czar — that we were previously told wasn’t necessary, he spoke with that odd dispassion of his, that maddening distance.

About the ban, he said, “I don’t have a philosophical objection necessarily.” About the czar, he said that it might be good to have a person “to make sure that we’re crossing all the T’s and dotting all the I’s going forward.” He’s talking theory and calligraphy while Americans are focused on blood, sweat and tears.

Ebola is his presidency in a petri dish. It’s an example already of his tendency to talk too loosely at the outset of things, so that his words come back to haunt him. There was the doctor you could keep under his health plan until, well, you couldn’t. There was the red line for Syria that he didn’t have to draw and later erased.

With Ebola, he said almost two weeks ago that “we’re doing everything that we can” with an “all-hands-on-deck approach.” But on Wednesday and Thursday he announced that there were additional hands to be put on deck and that we could and would do more. The shift fit his pattern: not getting worked up in the early stages, rallying in the later ones.