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Her challenge was to introduce herself to a curious nation while still fulfilling the traditional booster role the No. 2 slot requires.

She took to the role, slamming Mr. Obama and his running mate Sen. Joseph R. Biden Jr. for saying they’re fighting for Americans.

“Let us face the matter squarely. There is only one man in this election who has ever really fought for you, in places where winning means survival and defeat means death, and that man is John McCain,” said Mrs. Palin, whose 19-year-old son will be deployed to Iraq on Sept. 11.

She had the audience on its feet repeatedly.

“Amazing. Brilliant choice, spot on, everything we expected her to be,” said Chris Daniel, a delegate from Texas who said she “put it right to Biden and Obama.”

While Tuesday night’s session of the convention focused on Mr. McCain’s biography, Wednesday was more substantive, and taxes were at the forefront of the discussion.

Among the speakers, Republicans featured Christy Swanson, who with her husband owns a small business in Virginia filtering vegetable oils and reprocessing the waste to make biodiesel fuel. She was an Obama supporter until she heard Mr. McCain speak three months ago.

She said Mr. Obama’s tax plan, which would raise taxes on upper-income families, and therefore on many small businesses, would hurt.

“Quite frankly, higher taxes scare the biodiesel out of me,” she said.

Republicans also hit on energy, calling for an all-of-the-above energy policy that would include expanded drilling.

“Drill, baby, drill, and drill now,” former Maryland Lt. Gov. Michael S. Steele said.

Still, nobody mentioned the tricky issue of drilling in the Arctic National Wildlife Refuge, which Mrs. Palin supports but Mr. McCain opposes.

James Armstrong contributed to this article.