Newt Gingrich's horrible approval rating just keeps getting worse. A new CNN/Opinion Research poll finds that 63 percent of all Americans view Gingrich unfavorably, while only 25 percent see him positively. "Those are some seriously atrocious numbers," says Steven L. Taylor at Outside the Beltway, and they seem to "vindicate anyone who argued that Gingrich would implode" eventually. How could a candidate who once led in GOP polls have fallen so low? Here, four theories:

1. Newt's ethics problems still haunt him
"It was obvious to everyone who remembered the history of the 1990s that Gingrich would be a disaster as a presidential candidate," says John Hinderaker at Power Line. After Newt's brief stint as "man of the hour," his numbers have simply returned to where they were in 1997, when Gingrich was facing ethics troubles and a GOP backlash over his contentious tenure as speaker of the House. Voters haven't soured on Newt — they've just finally remembered what they thought of him in the first place.

2. Even his fellow Republicans hate him
Newt didn't get to be "the most disliked politician in America" by alienating Democrats and independents, says Aaron Blake at The Washington Post. Even among Republicans, his numbers are bleak. This trifecta is a "rare combination." Even at their "most divisive," George W. Bush, Sarah Palin, and Nancy Pelosi have had more friends. By establishing himself as an object of bipartisan derision, Gingrich has set himself apart.

3. Voters are fed up with his persistence
"Gingrich has been 'the zombie candidate' since Florida, where his decisive defeat abruptly halted whatever momentum he picked up in South Carolina," says Tina Korbe at Hot Air. Establishment Republicans want Newt to quit so he avoids damaging the ultimate nominee. And conservatives want him out so they can rally behind the surging Rick Santorum. But Gingrich's "appetite for the presidency" is too strong. Clearly, voters don't like that he insists on counterproductively fighting to the bitter end.

4. Romney's attack ads have taken a toll
Gingrich's biggest problem, says Kenneth T. Walsh at U.S. News & World Report, is that he was pummeled by attack ads from Team Romney. Along with the negative news coverage the ads stirred up, the attacks focused attention on Gingrich's troubles during his years in Congress, "his admitted adulteries, his changed positions on some issues, and his seeming arrogance." That did not endear Newt to voters.