Danforth said he wants to spend more time with his wife, who has reportedly been recovering from a badly broken ankle suffered in a fall.
"Forty-seven years ago, I married the girl of my dreams, and, at this point in my life, what is important is to spend more time with her," Danforth wrote in his resignation letter to the president, which was dated Nov. 22. "Because you know Sally, you know my reason for going home."
The 68-year-old former three-term U.S. senator from Missouri will leave his post on Jan. 20, shortly before the tentative date for holding elections in Iraq. Danforth became ambassador on July 1, succeeding John Negroponte who was named U.S. ambassador to Iraq.
According to The Washington Post, Danforth had recently expressed frustration over the effectiveness of the United Nations, particularly the U.N. Security Council, in dealing with world problems.
"While the U.N. is an important part of multilateralism, which is essential to U.S. foreign policy, it's very difficult to get strong resolutions passed," Danforth told the Post in a recent interview. "It's built for compromise, and it's built for wordsmithing. It's difficult to create real policies because of the ornate structure of multilateralism, at least the U.N.'s version of it."
The New York Times reported that Danforth had publicly expressed impatience with the U.N. General Assembly in late November after a resolution to denounce human rights violations in Sudan was blocked.
"One wonders about the utility of the General Assembly on days like this," Danforth said. "One wonders if there can't be a clear and direct statement on matters of basic principle, why have this building? What is it all about?"
Danforth further said, "The message from the General Assembly is very simple and it is, 'You may be suffering, but we can't be bothered.' "
Danforth also reportedly took issue with some State Department restrictions. According to the Reuters news service, Danforth said in a speech at Washington University in St. Louis that the State Department vetting process turned his official statements into "mush."
Danforth previously served as President Bush's special envoy to Sudan and is expected to still be in office for the planned December completion of a peace treaty between the Sudanese government and rebels who have fought a 21-year civil war.
In his letter to the president Danforth said he would be willing to undertake special assignments from the president in the future.
In an interview with the Post, Danforth said he felt his time in government service would be temporary.
"I'm not some government guy," Danforth said. "Really, what I am is Sally Danforth's husband and a Midwestern guy. And so in my own mind, I'm sort of on loan to do this for a little bit."
The New York Times reported that Danforth, an Episcopalian minister who officiated at former President Ronald Reagan's funeral in June, was known in Washington, D.C., as "Saint Jack," both for his stellar reputation and for his penchant for lecturing his colleagues on moral issues.