Our petition to the media urging McCain to get an Alzheimer's test received more email than usual, so let me address some of the issues raised with as much sensitivity as possible. 

Like most Americans, I've lost close relatives and friends to Alzheimer's. The very last thing I want to do is make that already-painful disease the slightest bit more painful for its victims, both direct and indirect. 

Here's the issue in a nutshell: obviously we can't choose whether or not to get Alzheimer's. But we can choose whether or not to put a man with decent odds of getting it into the most powerful job in the world, which includes second-by-second control over 10,000 nuclear weapons.

Alzheimer's afflicts an estimated 5.2 million Americans, 5 million of whom are over 65 (page 10). No one is exempt, as Ronald Reagan sadly proved. At present, Alzheimer's can't be cured, although some drugs show promise in delaying the effects.

Over the course of the campaign, John McCain has repeatedly exhibited memory problems. Last week, McCain struggled to answer how many homes he had. Before that, he couldn't remember the $1 million lawsuit he filed in 1990. He even seems to forget the U.S. invasion of Iraq in 2003. He repeatedly forgets the fact that Al Qaeda is Sunni not Shia, and that Czechoslovakia split into the Czech Republic and Slovakia in 1993.

Are these memory problems early symptoms of Alzheimer's? It's one possibility. Obviously there are other non-medical possibilities as well: dishonesty (not wanting to admit how rich he is), letting other people in his life handle various issues (like Cindy's fortune), failure to keep up with current events, learning difficulties (he ranked 894 out of 899 in his graduating class at Annapolis), and ideological blinders like those that persuaded every Republican to support George Bush's policies, no matter how wrong they were. McCain also takes at least two prescription drugs (Simvastatin and Ambien) that can affect memory.

But Alzheimer's isn't the only medical possibility. McCain could also be suffering from dementia (like Margaret Thatcher, who can't remember that her husband died) or a lesser condition called "Mild Cognitive Impairment."

There are many reasons to suspect McCain has a medical problem of some kind. Naturally, his age (72 this week) is a major risk factor. But McCain's brain has suffered a number of traumas that could affect cognition:

• Taking blows to the head as a competitive boxer for three years
• Heavy drinking as a young officer
• PTSD from his 5 plane crashes and torture as a POW

McCain also exhibits non-cognitive symptoms of brain injury, including his frequent bouts of rage aimed at fellow Senators and even his wife Cindy. This rage spills over to foreign policy issues, where his first response is often reckless and dangerous threats of war.

Given all of these issues, it is perfectly appropriate for the American people to ask whether McCain is mentally up to the enormous physical and mental demands of the Presidency of the United States - especially when we are at war in Iraq and Afghanistan, fighting Al Qaeda terrorists around the world, and possibly on the brink of war with Russia.

And the only way to answer those questions is a thorough neurological examination, including tests for cognitive impairment and dementia, which can indicate early Alzheimer's.