All this is not to say that Mr. Obama resembles the squashy caricature drawn by his opponents. He is actually constructively two-minded on the issue. He caught grief for proposing unilateral action against targets in Pakistan, which now appears to be Bush administration policy. And there is spine in his language, sometimes too much. In his convention speech, he said, “McCain likes to say that he’ll follow bin Laden to the gates of Hell  but he won’t even go to the cave where he lives.” I’m still not sure what this means, but it’s very muscular.

Barack Obama has also made useful proposals on nuclear matters, promising to secure the world’s loose fissile material in his first term. This is an over-idealistic goal, as it would require the cooperation of such countries as North Korea, Iran, Pakistan and, especially, Russia (though he’s better positioned to engage Russia on this subject than is the hectoring John McCain).

There is no one in Washington more sincerely gripped by the issue than John McCain, but he comes with his own set of problems on matters of counterterrorism, not least of which is his rhetorical excess, and his strange decision, given his (justifiable) preoccupation with the issue, to choose as his running mate the figurehead commander of the Alaska National Guard. Though Islamist terrorism might in fact be the “transcendent” threat of our time, as Senator McCain says, it is tactically imprudent to build up the already huge egos of our enemies, to feed the Islamist hope that they are, indeed, engaged in a clash of civilizations.

Years ago, in pre-9/11 Afghanistan, a leader of the Taliban’s morals police, the Committee for the Propagation of Virtue and the Suppression of Vice, asked me to describe just how much the Taliban frightened Bill Clinton. I told him not at all. In fact, Mr. Clinton was probably not frightened enough, but I wasn’t going to let on to that. Watching this man’s crest fall was a rare pleasure in Kandahar.

Senator McCain has other problems worth noting: an excess of incaution, perhaps, about pre-emption (in our conversations, the various surprises associated with the Iraq invasion had not caused him to calibrate at all his views on anticipatory defense); and a seeming inability, or unwillingness, to differentiate among Islamist terrorist groups.

I asked him not long ago whether he believes that America conflates its problem with Iran with Israel’s Iran problem. He said Israel’s existence is an American moral and national-security imperative. “I think these terrorist organizations that [Iran] sponsors, Hamas and the others, are also bent, at least long-term, on the destruction of the United States of America,” he added. “Iraq is a central battleground. Because these Shiite militias are sending in these special groups, as they call them ... to remove U.S. influence and to drive us out of Iraq.”

There are many different things taking place inside his answer, not all of which are connected. Hamas is a disgraceful group, ideologically opposed to most of what America represents, but it is unconnected to the fight against Shiite militias. These conflations, among other things, preclude serious conversation about ideology and motivation.

So what we have is one presidential candidate who still seems to be casting about for an overarching strategy; and another one who is not entirely sure whom we’re fighting. We can hope against hope that in the next two months, these two men will discuss, in a deliberative and encompassing way, the best ways to protect America from what some nonproliferation experts believe is a nearly inevitable attack. We should, in fact, demand that this conversation take place, because nothing else matters.