WASHINGTON (CNN) -- Former Republican Sen. Phil Gramm said Friday that he is stepping down as co-chairman of Sen. John McCain's presidential campaign amid criticism for saying last week that "we have sort of become a nation of whiners."

Phil Gramm, left, said his comments have become a "distraction" for Sen. John McCain's campaign.

Gramm on Friday said he would "join the growing number of rank-and-file McCain supporters."

Democrats blasted Gramm for the comments, made in a Washington Times interview published July 10, and McCain forcefully repudiated the remarks.

In a written statement released Friday, Gramm said his comments had become a distraction for McCain.

"It is clear to me that Democrats want to attack me rather than debate Senator McCain on important economic issues facing the country," Gramm said.

"That kind of distraction hurts not only Senator McCain's ability to present concrete programs to deal with the country's problems, it hurts the country."

Gramm, who advised presumed Republican nominee McCain on economic matters, made the controversial comments while discussing the economy.

"We have sort of become a nation of whiners. You just hear this constant whining, complaining about a loss of competitiveness, America in decline," the former Texas senator said. Watch Gramm explain his comments »

"You've heard of mental depression; this is a mental recession."

McCain responded that day to the comments saying during a campaign stop: "I believe that the person here in Michigan who just lost his job isn't suffering from a mental recession. I believe the mother here in Michigan or around America who's trying to get enough money to educate their children isn't whining."

A day after making the comments, Gramm said he was referring to America's leaders, not the public.

He stood behind the "mental recession" comment, though, saying, "we don't have measured negative growth. That's a fact; that's not a commentary."

McCain's Democratic rival, Sen. Barack Obama, said Friday that news of Gramm stepping down makes little difference.

"The question for John McCain isn't whether Phil Gramm will continue as chairman of his campaign but whether he will continue to keep the economic plan that Gramm authored and that represents a continuation of the polices that have failed American families for the last eight years," Obama campaign spokesman Hari Sevugan said.

Obama had been quick to jump on Gramm's comments last week, saying Americans need more than "psychological relief."

"I think it's time we had a president who doesn't deny our problems or blame the American people for them but takes responsibility and provides the leadership to solve them," Obama said at a Virginia rally shortly after the comments were reported. "That's the kind of president I will be."

All About John McCain • U.S. Presidential Election