WASHINGTON -- Responding to criticism from a Senate Democratic ally, President Obama explained why he fired the Inspector General of the AmeriCorps without the 30-day notification required by law, calling Gerald Walpin so "confused" and "disoriented" that there was reason to question "his capacity to serve."

In a letter to the bipartisan leaders of the Senate Committee that oversees AmeriCorps, Obama listed these alleged defects in Walpin's leadership as an Inspector General.

• Removed after unanimous request from the AmeriCorps board of directors
• At May, 20, 2009, board meeting Walpin "was confused, disoriented and unable to answer questions and exhibited behavior that led the board to question his capacity to serve."
• The U.S. Attorney for the Eastern District of California complained about Walpin's conduct to the IG oversight board and alleged he withheld exculpatory evidence.
• Walpin had "been absent from the Corporation's headquarters, insisting upon working from his home in New York over the objection" of the board.
• He "exhibited a lack of candor in providing material information to decision makers."
• He "engaged in other troubling and inappropriate conduct."
• He "had become unduly disruptive to agency operations, impairing his effectiveness."

The letter, authored by Norman Eisen, Special Counsel to the President for ethics, concluded: "It was for these reasons that Mr. Walpin was removed."

Hours before, Sen. Claire McCaskill, Missouri Democrat, criticized Obama for failing to specify why he fired Walpin.

"The White House has failed to follow the proper procedure in notifying Congress as to the removal of the Inspector General for the Corporation for National and Community Service," McCaskill said in a statement. "The legislation which was passed last year requires that the president give a reason for the removal. 'Loss of confidence' is not a sufficient reason. I'm hopeful the White House will provide a more substantive rationale, in writing, as quickly as possible."

Obama voted for the legislation requiring specific notification to Congress of the reasons to dismiss an inspector general. Any move to fire an inspector general requires 30-days notice. Obama voted for the law to strengthen the independence of inspectors general.

Walpin led a 2008 investigation into allegations of misused taxpayer funds distributed by AmeriCorps to the St. HOPE Academy of Sacramento, founded in 1989 by Obama supporter and former NBA player Kevin Johnson. Walpin said Johnson, now mayor of Sacramento, misused roughly $850,000 in AmeriCorps funds. His referral to the U.S. Attorney's Office did not result in the filing of criminal charges. But St. HOPE officials agreed, via a settlement, to repay half of its AmeriCorps grants.

On Tuesday, Rep. Darrell Issa, California Republican, sought all White House information Walpin's firing. That followed a request from Sen. Charles Grassley, R-Iowa, that AmeriCorps provide "any and all records, e-mail, memoranda, documents, communications, or other information" related to Walpin's firing. Issa and Grassley are minority members of congressional oversight panels.

Republicans also have asked what role, if any, First Lady Michelle Obama played in Walpin's firing. The White House denies she had any voice in Walpin's future with the agency.

Republicans began to question Michelle Obama's role after press reports indicated she was taking a strong interest in AmeriCorps activities and when her former chief of staff, Jackie Norris, became a "senior adviser" to the Corporation for National and Community Service, also known as AmeriCorps.