President Bush's nominee to be the U.S. ambassador to the United Nations got a show of support on Thursday from a veteran of high-stakes diplomacy, former British Prime Minister Margaret Thatcher (search).

"A capacity for straight talking rather than peddling half-truths is a strength and not a disadvantage in diplomacy. Particularly in the case of a great power like America, it is essential that people know where you stand and assume that you mean what you say. With you at the U.N., they will do both," Thatcher wrote Wednesday in a letter to John Bolton (search) obtained by FOX News.

The boost comes amid a squabble at the Senate Foreign Relations Committee over dueling demands for evidence from the State Department. Documents obtained by FOX News show that committee chairman Richard Lugar, R-Ind., discounted three Democratic requests as "extremely broad" and of "marginal relevance."

Ranking Democratic Member Joseph Biden disagreed and hinted that he might seek another delay in the panel's vote on Bolton if the State Department fails to honor both sides' requests.

At the White House, impatience with the Democratic probe is growing.

"There's a difference between responding to legitimate concerns and just people trying to go down the road of a fishing expedition," said White House Press Secretary Scott McClellan.

A central allegation against Bolton, the undersecretary of state for arms control and international security, is that he tried to punish intelligence analysts who opposed his views. Former assistant secretary of state John Wolf told Senate investigators, according to a transcript obtained by FOX News, that Bolton put "pressure" on employees and blocked dissenting views.

"Quite often, the protracted debate delayed getting issues to the secretary in a timely way," Wolf said of exchanges at the State Department.

Officials there flatly rejected the charge.

"He kept the secretary informed of what was going on in his area," spokesman Richard Boucher said of Bolton.

Anne Gruner handled arms control at the CIA for 25 years, rising to deputy director of WINPAC, the spy agency's intelligence unit on weapons of mass destruction.

Now retired, she served as Bolton's arms control intelligence adviser on several trips to Russia during his negotiations over the Moscow Treaty of Strategic Offensive Reductions.

Gruner depicted Bolton as a consummate professional, effective in his dealings with the Russians and appreciative of the work of intelligence analysts. She said that the Russians ultimately signed the treaty in large part because of Bolton's diplomatic skill, despite CIA intelligence analysts' predictions that an agreement would never be reached.

Gruner described how Bolton reacted when she sometimes rebuffed his requests to declassify data.

"A lot of times, I would have to say 'no' and that was fine. He didn't kick me out of the room or stop talking to me. It was very professional," Gruner told FOX News.

Democrats claim Bolton was contemptuous toward the analysts at the State Department's Bureau of Intelligence and Research (search) (INR). Gruner, however, recalled one instance in Moscow when Bolton was about to present material prepared by INR to the Russians. The material hadn't been screened by the CIA, as he had requested, a failing that made the undersecretary "very irritated," Gruner said.

"I certainly had the impression that he was not always happy with the support he got from INR," she said.

Late Thursday, word of a surprise endorsement for John Bolton came from from former Deputy Secretary of State Richard Armitage (search), a close ally of former Secretary of State Colin Powell, who was widely believed to be opposed to the nomination.

"John Bolton is eminently qualified. He's one of the smartest guys in Washington," Armitage told The Associated Press.

Click in the box near the top of the story to watch a report by FOX News' James Rosen.