"The fact of the matter, nonetheless, was that Vespasian and Mucianus had agreed on a plan of action already. When they received the news of Otho's accession, during Titus' absence, they decided to acknowledge him as their emperor, and administered the oath of allegiance to their troops forthwith. Neither of them was particularly enthused about Otho's cause. Rather, they were playing a waiting game, planning--according to Tacitus--to sit on the sidelines while Otho and Vitellius slugged it out. In their view, it did not matter which contender won the war, because both were so horribly flawed that the one would be brought doen by the war, the other by his victory. This is a classic example of a motif as popular with Greco-Roman historians as are conspiratorial theories of history today, that of the tertius gaudens, the third party who waits till a struggle between two other rivals has been fought, and the victor has been so weakened by his success that he can be defeated."
--Gwyn Morgan, 69 A.D.: The Year of Four Emperors at 180 (OUP 2006).
We are now in for five solid weeks of Hillary v. Obama, no holds barred. "Tertius gaudens" seems like a pretty good strategy for Sen. McCain, eh?