WASHINGTON (CNN) -- President Bush nominated former House Budget Committee Chairman Jim Nussle to replace Rob Portman as his budget director Tuesday after administration officials announced Portman's resignation.
Portman, of Ohio, won seven terms in the House of Representatives before Bush named him U.S. trade representative in 2005. He became head of the Office of Management and Budget in May 2006.
"Rob's a tough act to follow, but that's why I picked Jim Nussle," Bush said. "He's a man of integrity, a man of vision, a man well qualified to hold this job. I ask the Senate to act quickly on his nomination."
Two sources close to Portman told CNN that the former lawmaker has about $1.5 million in old campaign funds and is moving back to his home state to consider a run for governor in 2010. He is the third top Bush aide to resign this year, following White House counsel Harriet Miers and longtime Bush adviser Dan Bartlett.
Privately, Republicans say Portman's departure amid Capitol Hill's budget battles will be a blow to the White House. Officials there have said the budget director's close ties to Capitol Hill would be an important asset when Bush sought major immigration, health care and energy reforms.
House Majority leader Steny Hoyer, D-Md., praised Portman on Tuesday even as he blasted the Bush administration as "the most fiscally irresponsible administration in the history of our country."
"I believe that Rob Portman was one of the best members at the time when he served," Hoyer said. "I disagreed with him on a number of issues, maybe a majority of issues. But I believe Mr. Portman to be a person of keen intellect, a responsible legislator and a person with whom one could discuss substantive issues of important fiscal impact."
Nussle, of Iowa, has similar credentials. He served eight terms in Congress before running unsuccessfully for governor in 2006, and has been working as an adviser to former New York Mayor Rudy Giuliani's presidential campaign since January.
Tuesday, he promised Bush that "I won't let you down."
"If I'm fortunate enough to be confirmed, I feel confident that my experiences in Congress and as the House Budget chair have prepared me well for the challenges that lay ahead," Nussle said. "I'm excited to help tackle our nation's priorities and work again with my friends and colleagues in the House and Senate."
Senate Minority Leader Mitch McConnell said Nussle is an "excellent" pick.
"We all know Jim Nussle," said McConnell, R-Ky. "He knows a lot about the process. I think he was a good choice."
CNN's Evan Glass contributed to this report 
