Republican National Committee Chairman Michael Steele on Friday declared his opposition to the Afghanistan war, saying the nine-year-old conflict was of President "Obama's choosing," and that the mission is "probably a lost cause" – prompting at least one prominent Republican to call for his resignation.

Steele made the comments at a fundraiser in Connecticut just two days after the Senate unanimously confirmed Gen. David Petraeus as the new U.S. commander in Afghanistan. Petraeus is taking over for Gen. Stanley McChrystal, who was ousted over his and his aides' scornful remarks of Obama's national security team to Rolling Stone magazine, at a time when America's casualty rate in the war is at record high and the offensive is falling short of expectations.

"This was a war of Obama's choosing," Steele said. "This is not something United States had actively prosecuted or wanted to engage in."

The war in Afghanistan began shortly after the September 11, 2001, terror attacks, in the first year of President George W. Bush's first term. Obama, at the time, was a state senator in Illinois.

"It was [Obama] who was trying to be cute by half by flipping a script demonizing Iraq, while saying the battle really should be in Afghanistan," Steele said in his delivery, which was posted on YouTube. "Well, if he's such a student of history, has he not understood that you know that's the one thing you don't do, is engage in land war in Afghanistan? All right, because everyone who has tried, over a thousand years of history, has failed."

Steele's comments led William Kristol, editor of the conservative magazine The Weekly Standard, to call upon the GOP chairman to resign over the July 4 weekend as "an act of service for the country you love."

"At a time when Gen. Petraeus has just taken over command, when Republicans in Congress are pushing for a clean war funding resolution, when Republicans around the country are doing their best to rally their fellow citizens behind the mission, your comment is more than an embarrassment," Kristrol said in a letter to Steele.

"It's an affront, both to the honor of the Republican Party and to the commitment of the soldiers fighting to accomplish the mission they've been asked to take on by our elected leaders," he wrote.

"There are, of course, those who think we should pull out of Afghanistan, and they're certainly entitled to make their case," Kristol added. "But one of them shouldn't be the chairman of the Republican Party."

Erick Erickson, the editor of the popular conservative website RedState.com and an opinion driver among younger Republicans, also called for Steele's ouster.

"Michael Steele must resign. He has lost all moral authority to lead the GOP," Erickson said.

Fox News contributor Karl Rove, a senior White House adviser to former President George W. Bush called Steele's comments "boneheaded," saying the Afghanistan war was "chosen for us by the people who ran Afghanistan -- the Taliban and their allies, Al Qaeda."

Democratic National Committee spokesman Brad Woodhouse said it was "simply unconscionable that Michael Steele would undermine the morale of our troops when what they need is our support and encouragement. Michael Steele would do well to remember that we are not in Afghanistan by our own choosing, that we were attacked and that his words have consequences."

Steele sought later to clarify his comments by noting that Obama said on the presidential campaign trail that the U.S. should concentrate fighting the war on terror in Afghanistan, not Iraq.

"Now, as president, he has indeed shifted his focus to this region," he said in a written statement. "That means this is his strategy. And, for the sake of security of the free world, our country must give our troops the support necessary to win this war."

"As we have learned throughout history, winning a war in Afghanistan is a difficult task," he added. "We must also remember that after the tragedy of Sept. 11, 2001, it is also a necessary one. That is why I supported the decision to increase our troop force and, like the entire United States Senate, I support Gen. Petraeus' confirmation. The stakes are too high for us to accept anything but success in Afghanistan."

Steele has been prone to gaffes that have enraged congressional Republicans. In the last year, he predicted the GOP won't win House control this fall. He also drew GOP ire when he criticized fellow Republicans in a book that party leaders didn't know he was writing until it was published. His GOP critics were irked further when he told them to "get a life" and "shut up."

Earlier this year, his oversight of the RNC was called into question because of lavish spending, including money to entertain donors at a lesbian bondage club in Los Angeles.

The Associated Press contributed to this report.