Since John McCain named her his running mate, Sarah Palin has been the woman in the bubble. She has not held a press conference, and the McCain campaign has kept her almost completely off limits from questioners who may not show her proper "deference," campaign manager Dick Davis said. No matter what their political beliefs, voters should see this as dangerous. The public needs to know what she believes, how she thinks, how much she knows and whether she has the temperament and judgment the presidency requires.

Nine of the first 42 presidents were vice presidents who took office unexpectedly. One, Gerald Ford, did so after Richard Nixon resigned; four succeeded presidents who were assassinated; four served out the terms of presidents who died of natural causes. Statistically McCain, who could become the oldest person ever elected to the presidency, has a one in five chance of dying during his first term.

Despite his vigor and nonagenarian mother, McCain was a two-pack-a-day smoker for 25 years, according to CNN. He has also had four melanomas removed, including one that was invasive. Both factors lower his long-term odds.

Vice presidential candidates rarely affect the outcome of elections. That's why tickets with incredibly weak candidates - think Spiro Agnew and Dan Quayle - have prevailed. But this is one election when it should.

The walls around Palin have gone up for the same reason that the press has lost most of its once ready access to Barack Obama and, above all, to McCain. It's too late in the game - unless you're Joe Biden, the Democratic vice presidential nominee prone to gaffes - to risk making stupid statements or revealing ignorance.

The bubble is created because politicians, who love the press on their way up, loathe its scrutiny once they are near or at the top. It's far safer to peddle your candidacy with television ads, stage-managed rallies, friendly interviews, photo ops, and faux town-hall meetings with pre-selected audiences - as the McCain campaign is doing with Palin. But such venues don't provide the information necessary to cast an informed vote. That requires seeing a candidate under the pressure of questioning from well-prepared interlocutors.

Palin, who recently got her first passport, is engaged in a week-long cram course of meetings with world leaders at the United Nations. Initially, her campaign allowed photographers to attend at least a portion of the sessions but barred reporters who could record her questions and comments.

That policy changed after CNN and other news outlets announced plans to boycott coverage of her meetings unless journalists had a chance to produce something more substantive than photos of Palin with foreign heads of state. Access was granted, but it's too limited to permit judgments about what Palin does and doesn't know about the world and the forces at play in it.

A window into Palin's familiarity with foreign policy will open during the campaign's sole debate between her and Biden on October 2. In the end, though, that may not tell voters enough either. McCain and Obama, in their two formal debates, will be given two minutes to answer each question, followed by five minutes of discussion to allow give and take. At the McCain campaign's instance, Biden and Palin will get half as much time - just 90 seconds per question, followed by two minutes of discussion. The sound bites of information, some of it newly acquired, that format will produce are no way to measure a candidate.

Vice presidents may not change the course of elections. But when fate places them in the highest office in the land, they can change history. They need to be ready.