In a blow to Mitt Romney's presidential campaign, Sarah Palin said Sunday that she's "not convinced" the former Massachusetts governor is conservative enough to do Republicans' bidding in the White House.

Palin, the former governor of Alaska, said the GOP presidential field remains wide open because Romney's past positions on healthcare, abortion and other issues have been moderate-to-liberal, leaving Republicans confused about what he'd do as commander-in-chief.


"Most voters in the GOP, and Independents, we will want to see that candidate who we can trust will just inherently, instinctively turn right – always err on the side of conservatism," Palin said on Fox News Sunday. "I am not convinced [Romney is that person]. And I don't think that the majority of GOP and Independent voters are convinced, and that is why you don't see Romney get over that hump."

Palin alluded to recent polls that put former Pennsylvania Sen. Rick Santorum atop the GOP field, as well as Romney's tough stretch last week when Santorum shocked observers by winning three primary contests in a row.

"He [Romney] is still in the 30 percentile mark when it comes to approval and primary wins," she said. "He still hasn't risen above that yet because we are not convinced."

Palin said Romney – for all the years and millions of dollars he's spent campaigning – has failed "to articulate his solutions" to the issues that concern voters.

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Palin said Romney is "a great candidate" whose conservatism "is evolving." But the former vice-presidential candidate was also quick to note the strengths of the other three GOP contenders – Santorum, former Speaker Newt Gingrich (Ga.) and Rep. Ron Paul (Texas) – saying the ongoing debate has improved all of them.

"I honestly think that we have a good slate of candidates, the four of them all with their individual strengths," Palin said, "and I believe they're getting stronger, they're getting better, and that's what competition provides [and] that's why I want to see the competition continue."

On Saturday, Palin delivered a spirited address to the Conservative Political Action Conference, an annual gathering of about 10,000 conservative activists.

While the bulk of her address targeted President Obama, Palin also took a veiled shot at Romney, who has faced persistent questions from conservative activists about his record.

“Our candidate must be someone who can instinctively turn right to constitutional, conservative principles,” Palin said Saturday. “It's too late in the game to teach it or to spin it at this point. It’s either there or it isn’t.”

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Romney has faced a surge from rival Santorum who swept a trifecta of GOP nominating contests last Tuesday.

A Public Policy Polling survey released Saturday also showed Santorum with his first national lead, ahead of Romney by 15 points.

Santorum and Gingrich have both tried to present themselves as the conservative alternative to Romney.