An effective strategy for "closing" thoughtful undecided voters is to illustrate exactly how likely Palin would be to succeed to the White House during a new Republican first term. McCain has a reservoir of good will that he may be able to tap into in the final weeks; but Palin scares the hell out of just about everybody.
My favorite example is "The Red M&M Test": the chances of a first-term President Palin are the same as your next M&M being red. They're also the same as rolling doubles to escape jail in Monopoly, a rainy day in San Diego, or being delayed on two consecutive flights into Newark or O'Hare. They're about equal to the odds that the next car you see will be black, that your birthday this year falls on a Wednesday, or that, in a big game, Kobe hits consecutive "3"s down the stretch.
Some think the most fitting analogy is the likelihood of bad result in Russian Roulette.
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Her ascension would be more likely than you catching the flu next winter. And it would be far more likely than being dealt a "21" in Blackjack, or sharing a Zodiac sign with a stranger.
Finally, Palin taking over as Commander-in-Chief during a first term would be three times more likely than the next middle-aged man you meet being left-handed... which both candidates are.
BTW, these are conservative estimates, based on life expectancy from standard Social Security tables; they don't take into account McCain's health problems. Some actuaries say the odds are actually 1 in 4 (I used 1 on 6 or 7). And, for the record, 9 of our 42 Presidents were VPs who succeeded to the office unexpectedly.
Toss around a few of these and see what happens. People usually laugh for a second before the look of horror sets in.
And, if you need them, there are more examples in my full original Portfolio.com blog on this subject:
www.portfolio.com/views/blogs/daily-brief/2008/09/15/feeling-lucky-the-odds-of-a-president-palin.