There are bumps, and there are bumps. For starters, there’s the Bristol bump — the bump of pregnancy that put Sarah Palin’s teenage daughter all over the Web this week. There’s the Republican vice presidential candidate’s own bump — the triumphant bump of $7 million in cash Governor Palin pulled in for the McCain campaign the week the Alaskan was announced.

These two bumps obscure a third one: that mysterious bump in gross domestic product. On August 28, even as Senator McCain was eliminating Mrs. Palin’s competition from his list of potential running mates, the Bureau of Economic Analysis reported the American economy grew an annualized 3.3% in the second quarter.

For a nation that’s been telling itself it is in recession, that’s interesting news. Was it the stimulus-package spending? The soft dollar? More jobs than we thought? The enormous effort they had to devote to spinning the Bristol story left neither Mr. McCain nor Mrs. Palin time to talk much about that 3.3%.

This dynamic is typical. The Grand Old Party has talked itself into believing that “character” is going to win the White House. But character is a treacherous credential. One misstep, and it’s gone. John Edwards lost his in a nanosecond when reporters saw him coming out of the Beverly Hilton after visiting paramour Rielle Hunter. Even if a candidate manages to keep his reputation intact for the duration of a campaign — a near impossible feat, it seems — he can still fail.

That’s because character candidacies are all about damage control. Defending a rep for character requires so much political energy that there’s little time left to develop economic or foreign policy goals. The same character obsession that gets you campaign dollars and a nomination can hurt you in the general election or in office.

Take Mr. McCain’s own life, where sustaining the “straight talk” man of character has sometimes proven difficult. Mr. McCain’s POW ordeal made him the ultimate character candidate, yet the voters who first put him in the House and then the Senate had to overlook marital behavior not entirely different from that of Senator Edwards.

One reason Mr. McCain’s best shot at the White House comes at age 72, and not 62, is that it took a full decade for the character candidate to recover from the poor judgment he demonstrated in accepting contributions from Charles Keating, whose Lincoln Savings and Loan collapsed.

Consider the damage the character banner did to Republicans in another campaign, that of 1996. Then the Christian Coalition told the Republican Party that it wanted a character candidate, not a markets candidate. Social conservatives went around crowing that they had cut Steve Forbes off at the knees in Iowa. The result was that Senator Dole, a character candidate lacking pizzazz, was trounced by one of the sinning-est presidents ever, Bill Clinton.

Yet the same character preoccupation was present in the selection of first Mr. McCain, and now Mrs. Palin. The Iron Dog snowmobile race that Mrs. Palin’s husband won. The five children. The pro-life signal that the birth of Trig, her Down syndrome baby, sends. Sure, she has economic credentials, but in the Palin choice, character was king.

This gives the Bristol news disproportionate importance. The chatter as I type this is about Mrs. Palin’s decision to sign an Eagle Forum pledge on abstinence programs for teens. There’s a wonderful discussion going on about whether Mrs. Palin can be a good mother to baby Trig when she’s at the White House.

The Bristol development is providing the Democratic candidate, Barack Obama, with an unexpected chance to look magnanimous — Senator Obama noted that he was born when his mother was 18 and deemed Bristol’s pregnancy “off limits.” More importantly, the baby topic is already preventing Mrs. Palin from developing other ideas.

Independence in energy is more important for America than in the past, to put it mildly. And on Arctic National Wildlife Refuge, Mrs. Palin’s “drill, drill” plan is the best single idea of any candidate. She needs to expand it and present it nationally as her own.

Big spending and corruption are imperiling the Republican Party’s very future. Mrs. Palin has done some good work here: battling Frank Murkowski for the governor’s office, for one thing. Turning against the “Bridge to Nowhere,” for another. A Palin program to cut Washington pork would make voters take her seriously.

What about taxes? Right now, the very topic is unfashionable. Even some conservative analysts deem tax cutting yesterday’s philosophy. But the topic doesn’t seem so yesterday to those shareholders who are selling stock to realize capital gains this year to avoid the near-certain tax increase in 2009 or 2010. And they will be more relevant than global warming to Republicans if Mr. Obama delivers on his pledge to heap all his tax increases on the top 5% of earners.

In a CNBC interview, Mrs. Palin managed to move forward on the tax topic. She said, “Low taxes, of course we know, spur the economy. I’m a Republican. I am for low taxes.”

This is just her first step in an Iron Dog of a challenge: proving that McCain-Palin are the growth candidates of 2008. But even if the pair stick with the character emphasis, the campaign’s path is clear. To prove character, they have to fight the issues, and escape the character topic.

Miss Shlaes, a senior fellow in economic history at the Council on Foreign Relations is a columnist of Bloomberg News.