(CNN) -- Karl Rove, perhaps the most powerful White House aide in recent history, called it quits Monday, provoking some to declare a symbolic end to the presidency of George W. Bush.

Karl Rove was dubbed by President Bush as "the architect."

Known as "Bush's brain" by critics and "the architect" by Bush himself, Rove announced his resignation during a low point in the administration, with Democrats having taken control of Congress and after Bush's immigration and Social Security plans failed.

"This is the end of the Bush presidency, absolutely," said Wayne Slater co-author of a book on Rove titled "The Architect."

"All lame ducks are lame ducks; this one, with Karl Rove now turning out the lights, is the most lame duck we've seen in a long time."

Democratic strategist Donna Brazile, who holds a "grudging respect" for Rove and his accomplishments, said she didn't know whether his absence would push Bush "over the edge" into lame-duck status.

"To lose someone with Rove's ability is, I'm sure, very humbling," said Brazile. "There would be no Bush presidency without Karl Rove so it's hard to separate president Bush's legacy from that of Karl Rove."

GOP strategist Bill Bennett downplayed the effect of Rove's departure, saying it's not a "big blow" to the administration.

"There are limits to what the president can do now on the domestic front particularly. In his role as commander in chief there are other people that the president will rely on," said Bennett, who served under two Republican presidents.

With Rove facing a subpoena from a Senate committee investigating why U.S. attorneys were fired earlier this year, some people in the White House thought that Rove had become a distraction, reported CNN White House correspondent Suzanne Malveaux.

Bennett described Rove as probably the most influential senior aide to any president. "People tend to think of Karl Rove as a political strategist and indeed he is, one of the best we've seen, but he was also a policy guy," said Bennett.

Rove was often involved in meetings on major policy issues, gaining experience that would be extremely valuable to the current group of Republicans seeking the presidency. See how Rove has played a vital role in the administration from the beginning »

But Democratic strategist Stephanie Cutter said Rove's mistake was that he tried to "run the White House and the federal government like a campaign."

Rove left after White House Chief of Staff Josh Bolten requested that White House staffers resign before Labor Day or commit to serving the president through the end of his term -- January of 2009.

"But that won't stop people in Washington from saying Rove is abandoning the President," said CNN's senior political analyst Bill Schneider. Watch what Rove's resignation may mean »

"If Republicans want to consult with Karl Rove, they will do so very quietly behind the scenes," Schneider said. "But I think right now he's too explosive, he's too poisonous really, because of his association with a very unpopular president."

Rove was one of a group of loyal Texans who followed Bush to the White House after helping him win the state's governorship.

Another member of that group, former Bush aide Karen Hughes, called Rove "the Energizer bunny of the West Wing" because he was always upbeat.

"Karl is brilliant. He is funny. And he's a passionate advocate for the president and his policies," said Hughes. "And I know he'll continue to play that role outside the administration."

Bennett said he doubts that Rove would get involved in the upcoming presidential race.

"Wouldn't you love to track the phone lines this morning from the various campaigns?" Bennett said, smiling. "I wonder if any Democrats might call him?" E-mail to a friend

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