US President Barack Obama has admitted he "screwed up" after the withdrawal of two key government nominees over unpaid taxes. The messy political developments threatened to blunt Mr Obama's effort to take his economic message to the US through a series of TV interviews. Former senator Tom Daschle pulled out as Mr Obama's pick as Health and Human Services secretary, citing a growing chorus of criticism over his failure to fully pay taxes from 2005 through 2007. He has since paid more than $140,000 (£97,200) including interest. Mr Obama admitted making a mistake. He said: "I think I screwed up, and I take responsibility for it, and we're going to make sure we fix it so it doesn't happen again." The President said he wanted to assure the US that under his leadership there would not be "two sets of standards, one for powerful people, and one for ordinary folks who are working everyday and paying their tax." Mr Daschle's departure was a deep blow to the White House because it not only cost Mr Obama his services as a Cabinet secretary but removed him from the second important role he was to play in shepherding the administration's hopes of overhauling the nation's health care system. It came just hours after Nancy Killefer pulled her candidacy to be the first chief performance officer for the federal government, saying she didn't want her failure to submit payroll taxes for household help to be a distraction for the President. She had faced but subsequently settled a Washington city government tax demand of $946 (£656) on her home. Meanwhile, Mr Obama and First Lady Michelle Obama took time out to read to children at a primary school in Washington.