President Barack Obama's nominee for U.S. ambassador to Iraq withdrew his name Monday after Republican lawmakers questioned his suitability following revelations that he had engaged in an extramarital affair with a journalist who later became his wife.

Brett McGurk, a longtime Iraq expert who had served on the Bush administration's National Security Council, wrote to Obama and Secretary of State Hillary Clinton that he was withdrawing with a heavy heart.

I believe it is in the best interests of the country, and our life together, to withdraw my nomination and serve in another capacity, McGurk said in the letter, a copy of which was seen by Reuters.

The nomination was withdrawn one day before it was scheduled to be considered by the Senate Foreign Relations Committee. It is unclear whom the White House would nominate in McGurk's place, administration and congressional officials told The Wall Street Journal. His withdrawal throws a fresh question mark over Washington's uncertain relations with Iraq following the departure of U.S. forces last year.

As recently as Sunday, White House officials said Obama continued to stand by his nominee, 

McGurk's withdrawal ended weeks of speculation after emails surfaced that appeared to show that he had a romantic affair with Wall Street Journal reporter Gina Chon while both were stationed in Iraq.

The two have since married, and Chon has resigned from the Wall Street Journal.

But the emails drew criticism in Congress, where six of the nine Republican members of the Senate Foreign Relations Committee wrote to Obama requesting a new choice to head the huge U.S. Embassy in Baghdad.

Sen. Jim DeMint, R-S.C.,leader of the GOP opposition to the nomination, hailed McGurk's decision. He said the emails reinforced broader concern about his judgment and about whether he would undercut the country's moral authority abroad.

Now is not the right time to send someone who has that many questions to Iraq,  DeMint said.

Sen. Barbara Boxer, D-Calif., a senior member of the Foreign Relations Committee, said she hadn't yet decided how she was going to vote. I had issues and I was going to explore them, but it's unnecessary now, she said.

Another committee Democrat, Sen. Benjamin Cardin of Maryland, also had been uncertain about the nomination. His professional accomplishments were never in question, but there were some questions that had been raised that needed to be answered, he said.