WASHINGTON – There is a key metric for determining whether the attacks on Mitt Romney and the bruising GOP primary are damaging him for the general election: How is he faring among independent voters, now that they’re getting to know him better?

A breakdown of some numbers from the Jan. 22-24 NBC-Wall Street Journal poll shows that Romney’s unfavorability rating among independents has spiked 20 points in the past two months.

Among all Americans, the poll found, Romney is rated very or somewhat positively by 31 percent and rated very or somewhat negatively by 36 percent.

The office of pollster Peter Hart, a Democrat who helped conduct the survey, sent me the numbers among independents. While Romney’s positive numbers have been roughly stable, at just over 20 percent, there has been some change the past few months:

•In November, Romney was rated somewhat or very negatively by 22 percent of independents.

•In December, Romney was rated somewhat or very negatively by 29 percent of independents.

•And in the new poll, Romney was rated somewhat or very negatively by 42 percent of independents – 20 points higher than two months ago.

Also: In November, Romney was beating Obama 47 percent to 34 percent among those voters. Now the numbers are upside down: Obama beats Romney 44 percent to 36 percent.

Hart told me that Romney’s multiple gaffes, including revelations have led independents to start making a choice between Romney and Obama.

“Romney’s lack of connection with average people and Obama’s improving numbers on the economy account for the turnaround with independents,” Hart said. “It’s not as though they have said Bain has disqualified him or that he can’t be trusted because of his taxes – but this has created a gulf between him and the average voter. …

“When he was only the opponent of Obama, he was getting the independent vote as the alternative,” Hart said. “Now they see him in full relief, and they’re saying, ‘This isn’t my guy.’ ”