Herman Cain's latest presidential campaign implosion has put some of the Republican Party's most active voters in a distinctly uncomfortable position: deciding whether to abandon an accused adulterer to side with an admitted adulterer.

Even before Monday's allegation by an Atlanta businesswoman that she and Cain had a 13-year affair, the GOP contest was moving toward a two-man race between steady front-runner Mitt Romney and former House Speaker Newt Gingrich, the latest candidate to catch the fancy of the anti-Romney forces. That movement now is expected to hasten.