When she steps to the podium Thursday to debate Joe Biden, it'll be only a month since she was introduced to the nation, making her first national appearance as John McCain's running mate. Since then, her political stock has risen and fallen with a rapidity that makes Wall Street look stable. But as her own image may be slipping, she's helping others to enhance their own reputations.

It started with Charlie Gibson, who, not too long ago, was roasted widely on the Internet for asking questions deemed irrelevant while co-hosting a Democratic debate between Barack Obama and Hillary Clinton. Gibson got the first broadcast interview with Palin, who had wowed most observers with her prepared speech at the Republican National Convention.

Answering questions from Gibson, she seemed much less prepared -- and seemed especially clueless when asked about the Bush Doctrine. Gibson's ABC interview got tons of play, and was the first suggestion that limiting the Alaska governor's media appearances may be, at least partly, a defensive strategy.

Sean Hannity's Fox News interview with Palin came next, but was so loaded with softballs and puffballs, it veered between painful and laughable. (The laughs came courtesy of Jon Stewart, who excoriated Hannity, and drew huge laughs, merely by repeating the Fox News host's "fair and balanced" questions.

And when Katie Couric got to Palin, the woman whose strength is getting interview subjects to trust her scored the best -- and most important -- interview of her entire stint as anchor of CBS News. Merely by asking questions, sometimes repeatedly, that called out for clear answers and specific examples, Couric got something else instead.

If there were any lingering doubts that Palin, as a vice presidential candidate, had flubbed those two major media appearances, Saturday Night Live and Tina Fey obliterated them. After both appearances by Palin, Fey led that week's SNL broadcast with a scathing imitation of Palin. This past Saturday, Amy Poehler took the Katie Couric role, and all she had to do to make the audience howl was blink repeatedly in utter disbelief.

Fey, meanwhile, embarked on hilarious sentences to nowhere -- nonsensical filibusters that repeated words for the sake of repeating them. She looked wide-eyed and panicked, flashing a smile when all else failed -- and all else often did. It's the sort of bullseye comedy that can stick, and which Palin will have to work hard Thursday to overshadow and overcome.

Fey's caricature of Palin Saturday was, in essence, the political equivalent of that South Carolina Miss USA contestant's classic brain freeze about "the Iraq." The difference, of course, is that the teenager was just trying to explain foreign policy. Sarah Palin is asking to help shape it.