Most of the opposition to John Bolton has been based on his brutish hostility towards his coworkers and his obvious disdain for the United Nations. While this is reason enough, to not appoint him to the ambassadorship, there is also a much more pragmatic reason; he is a Failure on National Security
Fewer weapons-grade nuclear materials were secured in the two years after September 11, 2001, than in the preceding two years.
North Korea, which had two nuclear weapons, now has eight. Bolton's scathing insults of President Kim Jong Ill provoked a dangerous reaction from the North Koreans, who called Bolton "human scum" and a "bloodsucker" who was "not entitled to take part in the [six-nation] talks.. "We have decided," they declared, "not to consider him as an official of the US administration any longer nor to deal with him."
On Bolton's watch, Iran has increased its nuclear program. Alarmingly, Bolton often blocked former Secretary of State Colin Powell from receiving “information vital to US strategies on Iran,” according to today's Washington Post.
Bolton successfully pushed to cut funding for the Nunn-Lugar program to halt the proliferation of nuclear materials, and failed to conclude a Plutonium Disposition Agreement with Russia to eliminate 70 tons of weapons-grade plutonium.
It has been reported that John Bolton's abusive demeanor only fuels the support of the president, that he in fact wants to put a "junkyard dog" in the United Nations to "shake up the beaurocracy"... Once again, George Bush is placing politics over National Security