As Sarah Palin remains secluded in Arizona getting ready for tomorrow’s debate with Joe Biden, the doubts about her candidacy from the right side of the aisle are continuing to mount:

A month after Gov. Sarah Palin joined Senator John McCain’s ticket to a burst of excitement and anticipation among Republicans, she heads into a critical debate facing challenges from conservatives about her credentials, signs that her popularity is slipping and evidence that Republicans are worried about how much help she will be for Mr. McCain in November. Ms. Palin, the Republican vice-presidential nominee, flew to Mr. McCain’s ranch in Sedona, Ariz., on Monday for three days of preparation with a team of his aides — a sharp contrast to the less structured preparation that led up to the senator’s first debate. The amount of time and staff power being devoted to this was evidence of concern among Mr. McCain’s associates that Ms. Palin’s early triumphs — a well-received convention speech, her drawing of big crowds — have been overtaken by a series of setbacks, creating higher stakes for her in the debate Thursday with the Democratic nominee for vice president, Senator Joseph R. Biden Jr. of Delaware. “I think she has pretty thoroughly — and probably irretrievably — proven that she is not up to the job of being president of the United States,” David Frum, a former speechwriter for President Bush who is now a conservative columnist, said in an interview. “If she doesn’t perform well, then people see it. “And this is a moment of real high anxiety, a little bit like 9/11, when people look to Washington for comfort and leadership and want to know that people in charge know what they are doing.”

And it’s not just columnists like Frum who are worried, some Republican Party officials are as well:

“I think the Katie Couric interview shows that she needs to be briefed more on certain aspects,” said Jim Greer, the Republican chairman in Florida. “She continues to be viewed very positively by the base of the party, but she needs to demonstrate that she’s got the knowledge and ability to be president should the need arise.” (…) But Mike Murphy, who used to work as a senior adviser to Mr. McCain, said Ms. Palin’s performance in the campaign had underlined his argument that she was a bad choice for Mr. McCain. Mr. Murphy said he was skeptical that she could turn it around in one debate. “She has the opportunity to undo some of the damage with a very strong debate performance,” he said. “That’s plausible. We’ll just have to wait and see.”

Along the same lines, Kathleen Parker, a NRO who wrote negatively about Palin last week, reports that she has gotten a lot of negative mail from conservative true believers:

Allow me to introduce myself. I am a traitor and an idiot. Also, my mother should have aborted me and left me in a dumpster, but since she didn’t, I should “off” myself. Those are a few nuggets randomly selected from thousands of e-mails written in response to my column suggesting that Sarah Palin is out of her league and should step down. Who says public discourse hasn’t deteriorated? The fierce reaction to my column has been both bracing and enlightening. After 20 years of column writing, I’m familiar with angry mail. But the past few days have produced responses of a different order. Not just angry, but vicious and threatening. Some of my usual readers feel betrayed because I previously have written favorably of Palin. By changing my mind and saying so, I am viewed as a traitor to the Republican Party — not a “true” conservative. Obviously, I’m not employed by the GOP. If I were, the party is seriously in arrears. But what is a true conservative? One who doesn’t think or question and who marches in lock step with The Party? The emotional pitch of many comments suggests an overinvestment in Palin as “one of us.”

More importantly, Parker notes that they demonstrate just how bad public political discourse has become:

Such extreme partisanship has a crippling effect on government, which may be desirable at times, but not now. More important in the long term is the less tangible effect of stifling free speech. My mail paints an ugly picture and a bleak future if we do not soon correct ourselves. The picture is this: Anyone who dares express an opinion that runs counter to the party line will be silenced. That doesn’t sound American to me, but Stalin would approve. Readers have every right to reject my opinion. But when we decide that a person is a traitor and should die for having an opinion different from one’s own, we cross into territory that puts all freedoms at risk. (I hear you, Dixie Chicks.) (…) Our day of reckoning may indeed be upon us. Between war and economic collapse, we have enormous challenges. It will take the best of everyone to solve them. That process begins minimally with a commitment to engage in civil discourse and a cease-fire in the war against unwelcome ideas.

And that goes for both sides.