President Bush looks toward outgoing White House Deputy Chief of Staff Karl Rove after speaking Monday on the South Lawn of the White House in Washington. Rove, Bush's close friend and chief political strategist, plans to leave the White House at the end of August, joining a lengthening line of senior officials heading for the exits in the final 1 1/2 years of the administration.

Washington ? GOP guru Karl Rove, bearing the credit for President Bush’s rise to power and the blame for his loss of support, quit his post Monday as the most influential political strategist of modern times.

“I’m grateful to have been a witness to history,” said Rove, leaving Bush to spend his last 17 months in office without the loyal wing man known to administration critics as “Bush’s Brain.” Rove joins a growing list of Texas loyalists abandoning a twilight presidency.

Rove, 56, hugged Bush on the White House lawn and said they first discussed his plans to resign last summer to spend more time with his family.

“It always seemed there was a better time to leave somewhere out there in the future, but now is the time,” Rove lamented. Bush called Rove “a dear friend.”

Rove, whose title as deputy White House chief of staff understated his power, leaves amid a congressional probe into his role in the firing of nine U.S. attorneys. The prosecutors allegedly were axed because they wouldn’t carry out the Bush administration’s political agenda.

Rove also leaked the name of outed ex-CIA spy Valerie Plame.

His departure signals the further eclipse of a presidency already weakened because of the Iraq war and by the rapidly approaching end of Bush’s term, some GOP sources say.

“The one-armed president just lost his other arm,” said a senior GOP strategist. “Karl was into everything. He was the intellectual engine of the government, for better and at times for worse. There was nobody Bush needed more and relied on more than Rove. His leaving certifies that this administration really is over.”

Not all Republicans think the Bush presidency is sunk.

“The cheerful analysis is that Karl has already laid out the game plan for the next year,” said longtime Rove pal Grover Norquist, who heads the conservative group Americans for Tax Reform.

Rove told The Wall Street Journal the GOP has “got a very good chance” to keep the White House in 2008, especially if Democrats nominate Hillary Clinton.

“They are likely to elect a tough, tenacious, fatally flawed candidate,” he said, referring to Clinton. Her campaign brushed off the remark.

“Given Rove’s track record of predicting a landslide win in 2000 and GOP gains in 2006, we’re not too worried about his analysis,” spokesman Phil Singer said.

The much-ballyhooed political strategist claims he’ll all but skip the 2008 elections. “I don’t anticipate taking any formal role,” Rove said.

Still, he could become an informal adviser to one or more campaigns because “I’ve got friends in all of the campaigns,” he acknowledged.

After 14 years with Bush, Rove’s laurels include orchestrating Bush’s election victories and ultimately writing the script for the presidency. But those marquee moments are scarred by the 2006 Democratic takeover of Congress.

Rove was the most powerful member of a Texas troika of loyal Bush image-makers, along with Karen Hughes and Dan Bartlett. Hughes is now a top State Department official, and Bartlett quit earlier this year.

“It’s probably a personal loss for the president more than a political loss,” said GOP pollster Kellyanne Conway.

Rove departs with Bush’s job approval rating among the worst in history, though he predicts that will change. “He will move back up in the polls,” Rove said.