ST. PAUL, Minn. - This one was really different.
John McCain has flummoxed the leaders of his Republican Party and most of the media by picking Alaska Gov. Sarah Palin as his running mate. It's a choice no other candidate conceivably could have made - a typical McCain gamble, unpredictable in its consequences.
The least plausible part of the McCain camp's scenario for Palin is the hope that she will help capture dissident Hillary Clinton voters. If my reporting in New Hampshire and Colorado is right, there were fewer of those voters - even before the Democratic convention in Denver - than polls had suggested. After Bill and Hillary Clinton's endorsements of Barack Obama, the number shrank further, and those liberal women are not likely to be attracted to a hard-right conservative such as Palin.
This does not make Palin a bad choice. A Bush White House operative said that he can see Palin stumping repeatedly through the Midwest battleground states, pitting her own blue-collar background against the similar family story of Joe Biden, the Democratic vice presidential hopeful.
"She can talk to those worried workers and their families in Ohio, Michigan and Pennsylvania as well as he can," he said. "She is really one of them."
That may be true. But Biden combines his working-class background with decades of experience in foreign policy - a base of knowledge Palin cannot hope to match no matter how hard she crams for their Oct. 2 debate. Her credibility will be on the line that night in St. Louis, as will Biden's self-discipline. He cannot afford to condescend. She will have to know her facts.
But long before that, Palin will have to go out campaigning on her own and face media interviews - all the tests that make former McCain campaign consultant Mike Murphy describe her candidacy as "fragile."
Murphy, who was interviewed Sunday on NBC's "Meet the Press," was undoubtedly right in saying that Palin, with her staunchly conservative social views, will strengthen the ticket among the Republican base. The crucial question is whether her maverick reformer history - challenging the incumbent Republican governor and the scandal-stained GOP establishment of her home state - will overcome her almost total lack of credentials to be a successor to the president of a wartime country.
Here in this convention city, the initial shock at the choice of Palin has given way to a tentative hopeful prognosis - conditioned by the realization that she has yet to face her real tests.
The two-step reaction is best capsulized in the comments of a very smart veteran campaign operative, a New Hampshire delegate and early Mitt Romney supporter, who told me: "When I first heard, I was appalled. I thought we had forfeited the election. But then I got a call from my 22-year-old daughter. She's a pro-choice voter, just like I am. But she was very excited and enthused by this choice. She is captivated by Palin's life story, the way she has taken on the odds. She may be more acute than I am."
That's the reaction McCain is counting on, not just among Republicans but, importantly, among independents and women, where most of the undecided votes are. And without realizing it, Obama may have boosted the odds on this gamble paying off.
Obama began his campaign for the nomination as the outsider candidate, promising fundamental change in Washington and offering a post-partisan approach to politics. With time, he has come to be seen as a much more conventional Democrat, now half of a ticket based in Congress, the least admired institution in a widely scorned capital. Millions who saw his acceptance speech heard a standard recital of liberal Democratic programs.
By picking Palin, McCain has strengthened his reputation not as an ideologue, not as a partisan, but as a reformer - ready to shake up Washington as his hero, Teddy Roosevelt, once did. My guess is that cleansing Washington of its poisonous partisanship, its wasteful spending and its incompetence will become McCain's major theme.
The Democrats' great advantage is that they are not responsible for the pain and frustration that many voters have suffered in the Bush years. But if McCain and Palin can shift the focus to the future, they may be able to appeal to the "change" voters who will in the end decide the election.
E-mail nationally syndicated columnist David Broder at email@example.com.