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As Rick Santorum surges in the polls, the conventional wisdom is that the Romney machine is warming up an all out assault on Santorum like they did against Newt Gingrich in Florida.

The "nuke Newt" strategy may have worked in the short term, but recent polling shows just how problematic a purely negative campaign has been for Romney, especially among those independent voters Romney will need in November.

According to a Pew poll released Monday, Romney has lost 8 points among independents since November.

An ABC/Washington Post poll last week asked voters what they thought about what the GOP presidential candidates have been saying on the campaign trail.  Fifty three percent of independents disapproved, while just 35 percent approved. Almost a quarter of Republicans (23 percent) disapproved as well.

Romney got a big boost in the polls with his Florida win (he gained 10 points in Gallup polling), but it was short-lived. The latest Gallup poll shows the one-time frontrunner now tied with Rick Santorum who jumped 14 points in the week since winning in Colorado, Minnesota and Missouri.

Furthermore, the Romney camp has done a great job discrediting other candidates, but they haven't done nearly as good a job in defining their own candidate.

The Pew poll found that fewer Republicans see Romney as a "strong conservative" than they did in November.  "Three months ago, a slim majority (53%) of Republican and Republican-leaning voters said Mitt Romney was a strong conservative," the Pew polling memo states. "Today, 42% see him this way, while the number who say he is not a strong conservative has jumped from 33% to 50%."

Just 39 percent of Republicans think Romney "takes consistent positions on issues," an 8-point drop since November. And, more ominously for Romney, almost half of all GOP voters (a 15-point jump since November), think that Romney is inconsistent on issues.

Remember, Romney and his allies have outspent everyone else in the field. By a lot. That makes these numbers even more extraordinary.

So what can Romney do?

To be sure, the Romney campaign has to start "defining" Santorum. And, they'll certainly get some help with that from the pro-Romney SuperPAC which spent heavily on ads attacking Gingrich.

But, at some point, Romney also has to make a positive case for himself. He may never be able to convince some of the conservative elements in the party that he is "one of them," but he does need to let them know that he has a vision for his campaign - and his presidency.