As I’ve been noting here, one key metric to determine whether the prolonged GOP nomination process is damaging Mitt Romney’s general election prospects is his standing among independents, many of whom remain sour on Obama’s economic performance.

Today’s new Pew poll offers another installment. The topline is striking enough — it finds that Rick Santorum is surging among Tea Partyers and conservatives, again suggesting that they just can’t come to terms with Romney as the nominee.

But look, Romney is still likely to get the nomination, anyway. Which is why this slide among independents is also extremely noteworthy:

A month ago, 40% of independents said they would back Obama over Romney — today 51% say they would, while the number expressing support for Romney has slipped from 50% to 42%.

Over the course of the campaign, Romney’s image among independent voters has suffered substantially. Most notably, the number who believe he is honest and trustworthy has fallen from 53% to 41%, while the number who say he is not has risen from 32% to 45%.

And even on his qualifications for the office — omney’s strong suit — he has lost ground among independents. In November, a 58% majority of independents said Romney was well-qualified to be president, while just 31% said he was not. Today, 48% say he is well qualified, while 41% say he is not.

In November, Romney was beating Obama among these voters, 53-41. Now those numbers are upside down: Obama is beating Romney among them, 51-42. That’s a net 19 point swing of independents in Obama’s direction in three months.

This comes after a recent NBC/WSJ poll found a 20 point spike in negative impressions of Romney among them. Democratic pollster Peter Hart’s diagnosis continues to ring true:

“Romney’s lack of connection with average people and Obama’s improving numbers on the economy account for the turnaround with independents,” Hart said...

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

I continue to believe that Romney will have plenty of time to reintroduce himself to these voters on his own terms, if and when he becomes the nominee. But among Republicans who are currently evaluating whether Romney is really more electable than Santorum, this should raise some bright red flags, and suggests again that Romney’s weakness as a general election candidate may have been papered over by his foes’ far more glaring and obvious weaknesses.