After spending the week at his Texas ranch, Bush resumes campaigning this weekend with a bus tour of battleground states and a new message. "We have turned the corner, and we are not turning back," he says in a new stump speech, excerpts of which were obtained by The Associated Press.

Kerry began the week tied or slightly ahead of Bush in the polls, a strong position for a challenger. Whatever sort of surge in support he receives from four days of his highly choreographed convention, Republicans hope to counter next month when they meet in New York to nominate Bush and Vice President Dick Cheney for re-election.

In his speech, Kerry painted a portrait of a nation suffering economically after four years of Republican rule.

"Wages are falling, health care costs are rising and our great middle class is shrinking. People are working weekends; they're working two jobs, three jobs and they're still not getting ahead," he said.

"We can do better and we will. We're the optimists," he said, and added, "We value an America where the middle class is not being squeezed, but doing better."

Kerry's decision to question the president over Iraq comes at a time when Bush is struggling to reverse a decline in support for his policies in a conflict that has claimed more than 900 lives, many of them since the president stood on an aircraft carrier beneath a banner that proclaimed "Mission Accomplished."

A Pew Research Center survey earlier this month showed 42 percent support for Bush on the war, down from 59 percent six months earlier.

But Kerry expanded his criticism far beyond Iraq as he sought to draw a contrast with the president on the national security issues he has placed at the core of his challenge for the White House.

"In these dangerous days there is a right way and a wrong way to be strong," he said.

"Strength is more than tough words," Kerry added in a slap at Bush without mentioning the commander in chief by name.

"I will immediately reform the intelligence system so policy is guided by facts, and facts are never distorted by politics," he said in reference to claims that the president relied on faulty intelligence in deciding to invade Iraq in 2003.

"And as president, I will bring back this nation's time-honored tradition: The United States of America never goes to war because we want to, we only go to war because we have to," Kerry said.

Kerry voted in October 2002 to give Bush the authority to use military force to topple Iraqi leader Saddam Hussein, but later voted against legislation providing $87 billion for Iraq and Afghanistan.

Kerry's convention scriptwriters supplemented the speech with a biographical video pitched to voters who will choose a president come fall.