President Obama won praise for overseeing a White House transition that started off smoothly and proceeded at record pace, with most of his Cabinet nominated within two months of the election.

But after three of his nominees withdrew their nominations over embarrassing revelations, questions have been raised about Obama's vetting process.

Tax problems forced former Sen. Tom Daschle, who would have headed the Department of Health and Human Services, and Nancy Killefer, nominated as a government performance officer, to withdraw their names Tuesday. And a pay-to-play investigation in New Mexico knocked Gov. Bill Richardson out of contention for commerce secretary last month.

Obama aides said Wednesday the president made more than a simple mistake in trying to save Daschle's nomination.

"I think in the interest of getting those appointments, the president trumped the principles he laid out in the campaign and he took responsibility for that," White House spokesman Robert Gibbs said.

Media focus on the two withdrawals has distracted attention from the economic stimulus package that the president is trying to sell to skeptical Republicans.

"They are all scrambling around defending themselves when they should be out selling their spending package," GOP consultant Terry Holt said, adding that most Washington insiders know the wheels are coming off the stimulus bill.

Vetting expert Ken Gross feels each of the nominees may have held back information.

"The thing that you're trying to avoid above all is surprises," he said. "And its surprises that are the killers."

The Obama vetting questionnaire was the most intrusive ever, going well beyond tax and income questions to ask about potentially embarrassing emails and blogs. Republicans say the president may be finding it difficult to achieve the high standards he's trying to set.

"When you set a high bar, you got to get over it," Holt said.

Yet on Wednesday, a day after replacing Richardson as commerce nominee, Sen. Judd Gregg confirmed an ex aide is under investigation in connection with disgraced lobbyist Jack Abramoff.

Gibbs said Gregg's not a target and he admits the president's own aides won't always meet his ethical standards.

"And I can assume that when that happens, I'll come in here and you get the sticks and I'll be the pinata," Gibbs said.

FOX News' Wendell Goler contributed to this report.