Despite his pee-pants performance in the Omaha debate against Lloyd Bentsen, it looks as if Dan Quayle, 41, will be president one of these days. Consider the politico-actuarial probabilities. Assuming the Republican lead endures, the junior senator from Indiana will be elected vice president. This alone will give him an even chance of becoming president. Three out of the last five presidents were vice president first. Seven out of the last ten vice presidents have ended up heading a national ticket, and four (five if you presumptively count George Bush) got all the way to the Oval Office.