US officials have launched a search for a new homeland security secretary after President George W Bush's first choice, Bernard Kerik, pulled out.
Mr Bush is said to have respected Mr Kerik's decision to withdraw
Mr Kerik cited tax and immigration queries about his employment of a nanny as his reason for withdrawing.
Former New York Mayor Rudolph Giuliani apologised to the president, having earlier backed Mr Kerik for the job.
Separately, President Bush named ex-Utah governor Michael Leavitt as his new health and human services chief.
If his nomination is approved by the Senate, Mr Leavitt, who currently heads the Environmental Protection Agency, will take the reins of one of the biggest government departments.
The soaring cost of health care and the millions of Americans without health insurance are likely to be among his immediate concerns, correspondents say.
'Apology not necessary'
White House spokesman Scott McClellan told reporters Mr Kerik had made a personal decision to withdraw his nomination and President Bush respected this.
1986: Joined NYPD as beat officer
1991: Awarded medal for valour after shoot-out
1997: Rose to rank of commissioner
2001: Oversaw department during 9/11
"We are moving forward to name a new nominee as quickly as possible," he said.
He also dismissed suggestions that the withdrawal of Mr Kerik had affected President Bush's relationship with Mr Giuliani.
"I know [former] Mayor Giuliani has expressed his apologies, but I don't think the president viewed that one was necessary," he said.
The homeland security department was created in the wake of the 11 September 2001 attacks on New York and Washington and employs more than 180,000 people.
Finding a replacement to its first chief, Tom Ridge, is seen as one of the key moves for the Bush administration as it heads into a second term.