Barack Obama’s presidential campaign is criticizing Republicans for going too negative at their convention.

A senior official for the Obama campaign said the attack-dog speech by former New York City Mayor Rudy Giuliani and the stinging remarks by GOP vice presidential candidate Sarah Palin could haunt Republicans in November.

Gibbs said that when a candidate emphasizes the contrasts between two politicians, as Palin did repeatedly in her address, “it’s not a zero sum game.” He said some viewers will end up seeing the Alaska governor more positively, but others will end up thinking of her more negatively.

Gibbs said he was struck by the tone of the attacks from Palin and Giuliani, who both mocked Obama’s background as a community organizer in Illinois.

“I think some of those lines are lines that largely will go over the heads of those who haven’t been focused on this election,” Gibbs said. He said he believed Giuliani, who energized the Xcel Energy Center crowd on Wednesday, used too much sarcasm in mocking Sen. Obama (D-Ill.), and said this could “turn off voters who will decide this election.”

Speaker after speaker has gone after Obama aggressively at the GOP convention.

Before Giuliani took the stage, former GOP presidential candidates Mitt Romney and Mike Huckabee both made comments directed at the Democratic presidential nominee. Romney even took a shot at Michelle Obama, highlighting her remark about being proud to be an American for the first time because of her husband’s political success. Romney said there had never been a day when he was not proud to be an American.

A day earlier, former Sen. Fred Thompson (R-Tenn.) ripped Obama before a roaring partisan crowd, and Sen. Joe Lieberman (I-Conn.), the Democratic vice presidential candidate in 2000, offered a dim view of Obama’s Senate accomplishments.

Democrats went after McCain at their own convention last week, and Obama was particularly critical of McCain’s positions in his speech that closed the convention. But Democrats also praised McCain as a war hero who had sacrificed for his country. Sen. Joe Biden (D-Del.) even drew applause for McCain from the crowd during his primetime speech.

Republican speakers have praised Obama’s patriotism and his eloquence, but so far there have been no applause lines.

Republican delegates on Thursday clearly loved both the speeches by Giuliani and Palin, who has become the star of the convention. But Gibbs said it remains to be seen how swing voters in America’s suburbs who are just getting to know Palin from television coverage will think.

He also said he did not think Republicans had done enough to introduce McCain to the country. While he has served four terms in the Senate and ran for president in 2000, Gibbs said much of the country still doesn’t know what he stands for.