We talked over the weekend about Mitt Romney’s “likability problem” — the more voters see him, the less popular he becomes. As the campaign progresses, this appears to be getting worse.

The number of Americans with negative views of Mitt Romney has spiked in a new Washington Post-ABC News poll, compounding the former Massachusetts governor’s challenges as he tries to rally from Saturday’s big loss in South Carolina.

Among independents, Romney’s unfavorable rating now tops 50 percent — albeit by a single point — a first in Post-ABC polling back to 2006. Just two weeks ago, more independents had favorable than unfavorable views of Romney; now, it’s 2 to 1 negative.

Romney’s losses since a Post-ABC poll conducted between the Iowa caucuses and the New Hampshire primary are not limited to independents. The number of Democrats viewing him unfavorably is up 10 percentage points, and among his fellow Republicans, negative ratings have jumped from 18 to 32 percent. (Prior to his Iowa performance, Romney’s unfavorable number had been higher than 18, but hadn’t been in the 30s among Republicans since early 2008.)

What’s striking is the speed with which this is happening. Just two weeks ago, Romney had a higher favorable than unfavorable rating. Now, the unfavorable number has soared, going from 34% to 49% in 16 days.

For much of the Republican establishment, the argument has been that Romney is a much stronger general-election candidate because Gingrich is so unpopular with the American mainstream. But as of now, the two leading GOP candidates have nearly identical fav/unfav numbers: 31/49 for Romney, 29/51 for Gingrich.

There are competing theories to explain Romney’s deteriorating standing — the criticisms of his work at Bain, his stilted persona, greater public awareness of his dramatic flip-flops, his shameless dishonesty, etc. — and it’s likely a combination of factors. Regardless, it’s tough to see these polls and think an extended nomination fight is in Romney’s best interests.

In the meantime, President Obama’s favorability rating — not his approval rating, just those with a positive impression of him — is now up to 53%, the highest it’s been since April 2011. That’s not what Team Romney wanted to see, either.

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.