Gingrich is now the third most likely Republican nominee–still way behind Romney, but just behind a still falling Perry. Thanks to his tenure as House Speaker, Gingrich is the most thoroughly vetted of all of the potential nominees. Of course, Americans have notoriously short-term memories when it comes to politics; Gingrich resigned in 1998 amid very low popularity following the government shutdowns of 1995 and 1996 and the perceived hypocrisy surrounding the Monica Lewinsky scandal and President Clinton's impeachment. You can still expect his far from scandal-free personal life to be a major issue for the religious right as social conservatives weigh his candidacy going forward.
Yet, despite such baggage, the good news for Gingrich is that the field of likely anti-Romney candidates is steadily thinning–leaving him the likeliest candidate for reconsideration among conservative GOP voters. Ron Paul is a libertarian and while he has maintained consistent support and attracted a passionate following, he has not broken into the mainstream of Republican conservatism. Jon Huntsman has been running as a moderate, gaining no traction with the Republicans. And Michelle Bachman and Rick Santorum have positioned themselves as hardline conservative candidates–in a way that has so far prevented them from garnering serious support outside the social-conservative camp.