There is one reason the job of vice-president exists. In a system with a single executive, you need someone to fill in if the president is incapacitated or dies. In war time this is especially important. More salient: McCain just turned 72 and would be the oldest first term president in American history with four cancer scares and the awful residue of Vietnamese torture in his bones.

The pick is also the first presidential-level decision a candidate has to make. You learn a lot about the candidate. And with Obama and McCain, we have two men who have never been executives - just legislators, book-writers and celebrities. So the decision is the first time we can compare the two men on a presidential decision level.

In Joe Biden, Obama revealed his core temperamental conservatism. It was a safe choice of someone deeply versed in foreign policy, and with roots that connected to the working class white ethnics he needed. It wasn't flashy; and was even a little underwhelming; but it was highly professional.

What we have learned about John McCain from his selection of Sarah Palin is that he is as impulsive and reckless a decision-maker as George W. Bush. We know this not because of what we have learned about this Pentecostalist populist since she exploded on the scene last Friday morning (and God knows we have learned more than we ever wanted). We know it because of how McCain made the decision. He wanted his best friend, Joe Lieberman, the former Democratic vice-presidential candidate for Al Gore. That pick would have been remarkable for its bipartisan nature, would have impressed independents, and signaled a centrist presidency centered on foreign policy. It would have been bold while not being rash.

But McCain is in charge of a party that is now, at its core, religiously motivated. Joe Lieberman, for all his political talents, is Jewish, pro-choice on abortion, gay-inclusive, and domestically liberal. McCain faced an insurrection in his party base if he picked him. Without the evangelical base, he wasn't going to win.

So last week, McCain picked someone he had only met once before. I repeat: he picked someone he had only met once before. His vetting chief sat Palin down for a face-to-face interview the Wednesday before last. It's very hard to overstate how nutty and irresponsible this is. Would any corporate chieftain pick a number two on those grounds and not be dismissed by his board for recklessness?

The recklessness was much more fatal in the new media world than in the old one. In the old media world, the Republicans could try to control the flow of information, browbeat the press and prevent the entire weird family background and series of scandals and rumors of quite incredible events from getting into the mainstream. But those days are over. Within minutes of the announcement, everyone reached for Google. I recommend for starters the two following stories that appeared in the Anchorage Daily News last March and April. Story 1 / Story 2

WIthin hours, the McCain campaign was under siege, as the vetting process the professionals didn't do was done by thousands of bloggers and citizen journalists. Palin's reality show family life, her vendetta against her ex brother-in-law, her endorsement of a mayoral candidate who ran against her own mother-in-law, her attempt to ban books in her local library, her friendship with one of her husband's former business partners, and on and on: this was the first major campaign event that was covered by the underground media before it reached the mainstream. The American mainstream press spent a large part of last week wondering how much truth the public could bear to hear.

McCain's entire campaign, moreover, was based on his superior experience to Obama, who was allegedly too unknown and risky for the Oval Office, and too jejune on foreign policy. And then McCain turned around and picked a total unknown who had been a mayor of a town in Alaska of a few thousand and then had only just got elected as governor of a very strange state with 700,000 people. More to the point, there is virtually no record anywhere of her views on foreign policy in the public record.

There is one documented instance. It came in an interview with the Alaskan Business Monthly in December 2006. She was asked about the central issue of McCain's campaign: the surge in Iraq, which he championed. She said she hadn't focused on the war with Iraq but had heard about the surge "on the news." She then said that she hoped there was an "exit plan." That was it. So on the central issue of McCain's campaign, Palin took the opposite position to John McCain.

McCain's major domestic issue in the election, moreover, is the economy and the rocky time many middle class Americans are having. All the polls show that he needs to offer something tangible to counter Obama's reconstructed Clintonomics and universal healthcare. By his own admission, he has never been that interested in economic issues. And his vulnerability is the sense that he doesn't get how distressed many Americans feel. So who does he pick? A governor whose state is essentially an oil company and whose major problem in the two mintes she has been in office has been what to do with a $5 billion oil surplus! She decided to send half a billion dollars' worth of checks to every Alaskan this summer. And people wonder why she's popular in her state.

It would be very hard to pick a governor in America who knows less about the struggles of most Americans in the current economy. Alaska's economy is currently like Russia's: booming because of commodity prices. And her one key policy issue in Alaska has been drilling for oil in the protected Alaskan National Wilderness Reserve - a policy McCain, against most of his Republican colleagues, has always opposed! Oh, and she's against protecting the polar bears as well. This is McCain's green conservatism: building pipelines, drilling in protected wildernesses and screwing the polar bears.

There are other obvious liabilities with Palin. To say the very least, her private life and family are colorful. The rumors about them do not stop coming, and the tabloid press has only just arrived in what can only be called Arkansas with penguins. Palin, moreover, currently has two ethics investigations into her conduct in the 18 months she has been in office - and one report is scheduled to go public days before the election. What was McCain thinking? And Palin's edcuation? Six colleges in five years ending in a degree in sports journalism from the University of Idaho. That's the background of someone who could be president of the United States at any moment after next January.

Who does John McCain think he's kidding? And what on earth was he thinking? This was a rash, impulsive, reckless pick. We have no idea where it's headed - and i wouldn't hazard a wild guess what we will have found out about Palin in a week's time. Maybe it will win some votes from evangelicals. Maybe Palin will reveal herself as something more than a former sportscaster who can deliver a speech. But it shows a deep unseriousness about governing the most powerful nation on earth at a time of great peril.

If you thought a president who went to war on flawed intelligence with no plan for the aftermath was reckless, then I have news for you. You haven't seen anything yet. Imagine the kind of decision-making McCain has just demonstrated applied to ife-and-death decisions with respect to Iran and Russia.

Yes, you have permission to be afraid.

Read www.andrewsullivan.com for daily updates

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