With Alaska Gov. Sarah Palin spending more time in front of the cameras as Sen. John McCain’s running mate, it’s starting to become clear why the McCain campaign has wanted to keep her under wraps. She’s just not presidential material.

It’s not a particularly shocking revelation to those who followed her career in Alaska, where she is known as a temperamental, secretive and heavy-handed executive. In the days and weeks since McCain asked her to join the Republican ticket, the liberal blogosphere has underscored her faults and failings, based largely on her record in Wasilla and Juneau.

As everyone knows, Palin immediately shored up the Republican base and brought excitement to the ticket that McCain could not. She was everything the GOP needed — youth, enthusiasm and sincerity. Her supporters raked her detractors, asserting she was indeed the real deal, a maverick in the McCain mold, a true-blue conservative and the ultimate New Woman. If Democrats were incapable of finally breaking the glass ceiling, Palin’s new-found supporters said, well by God, the Hockey Mom would show them how it’s done.

Some Republicans were overheard questioning McCain’s choice after it became clear how little Palin had been vetted and how ill-equipped she seemed to take over the reins if McCain could no longer serve. Charles Gibson’s interview on ABC gave many Americans their first view of the potential 45th president; Palin came off like a student who didn’t know the material but who clearly had been cramming.

Most reporters were kept at bay. But Katie Couric’s interview with Palin this week on CBS showed the VP nominee still has a lot of cramming to do, as she stumbled over her words, her facts and her ideology.

Conservative New York Times columnist David Brooks already raised the questions about Palin’s place at the presidential table. “Sarah Palin has many virtues. If you wanted someone to destroy a corrupt establishment, she’d be your woman,” he wrote last week. “But the constructive act of governance is another matter. She has not been engaged in national issues, does not have a repertoire of historic patterns and, like President Bush, she seems to compensate for her lack of experience with brashness and excessive decisiveness.”

Today, conservative National Review columnist Kathleen Parker said roughly the same thing, but her message seems to have more authority coming, as it does, from a woman who had been an early Palin supporter.

“It was fun while it lasted,” Parker writes. But having watched the Gibson, Sean Hannity and Couric interviews, it is clear that Palin is in over her head, she says. “Only Palin can save McCain, her party, and the country she loves,” the column continues. Parker asks the GOP’s first woman vice-presidential candidate to step aside.

“Do it for your country,” Parker writes.

Amen.