[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/04/20/art.zinnie0420.gi.jpg caption=" Retired Gen. Anthony Zinni was offered and accepted the post of U.S. ambassador to Iraq. Then, the offer was taken back with no explanation."]
WASHINGTON (CNN) - Chris Hill is slowly overcoming GOP opposition that has delayed his nomination as U.S. ambassador to Iraq, but it's still unclear why the Obama administration revoked the offer they gave to someone else first - General Anthony Zinni.
Zinni told CNN Monday he hasn't been given any explanation about why the offer he got in January for the post, which he accepted, was abruptly taken back.
Zinni confirmed in an e-mail that he was asked to take the job by Secretary of State Hillary Clinton, and even congratulated by Vice President Joe Biden. But then, the offer was revoked and extended to Hill - a development Zinni says he heard on the news.
Zinni is a retired four-star Marine general and former head of Central Command. Like President Barack Obama, he was an early critic of the Iraq war.
Sen. Lindsey Graham, R-South Carolina, told CNN he would have wholeheartedly supported Zinni for position because of his knowledge of the region. Graham, along with Sens. John McCain, R-Arizona, and Sam Brownback, R-Kansas, have led the opposition to Hill, citing his "controversial legacy" as point man in the six-nation talks aimed at dismantling North Korea's nuclear program and his lack of experience in the Middle East.
Graham, however, voted Monday to move Hill's nomination forward, while McCain did not vote. Brownback voted against Hill.
A State Department spokesman had no comment on Zinni.
A senior Democratic congressional source, who would not be quoted speaking about private deliberations, called the decision to nominate Hill over Zinni one of the "great mysteries" of the early days of the Obama administration.