John Bolton’s tenure as America’s U.N. ambassador was, by any measure, a remarkably successful one. But a group of senators implacably opposed to Bush’s foreign policy has spent the past year refusing to assess his work fairly, and has finally succeeded in ensuring that he will never be confirmed in his post. So with his recess appointment set to expire along with the 109th Congress, the ambassador departs — and we are the worse for it.

Bolton, you will recall, was first nominated in 2005. He had more than enough support to win confirmation by the full Senate, but a few members of the Foreign Relations Committee moved heaven and earth to block a floor vote. Their justifications were never convincing. The main contention was that Bolton was not awestruck by the U.N. — as much of the liberal establishment is — and had never been shy about criticizing it when criticism was due. This ought to have been reckoned a merit. In addition, Joe Biden threw a temper tantrum because the White House, citing executive privilege, would not release intelligence documents related to Bolton’s prior post at the State Department. (Bolton, it is worth noting, favored releasing the documents.) And Republican George Voinovich opposed Bolton in a teary-eyed speech for reasons that only George Voinovich understands.

It was clear through all of this that the real problem with Bolton was the administration he was to represent. Derailing his nomination was simply a convenient way of attacking President Bush’s foreign policy. And that is why, after Bolton had spent a year at the U.N., his critics made no serious effort to assess his achievements as ambassador, preferring instead to recycle their spurious attacks on his character. (Voinovich corrected his error and announced that he would now support Bolton. Too late, though, senator: Were it not for your folly a year ago, Bolton would not have had to resign this week.)

In recent hearings, the closest committee Democrats came to making a cogent argument against Bolton was quoting other diplomats’ anonymous smears of him. His aggressive style, said they, had alienated U.S. allies and set back the cause of U.N. reform. To this the obvious reply is 1) that Bolton’s critics provided not the slightest evidence that reform would have been achieved with a different ambassador representing the U.S.; 2) that reform is highly unpopular at the U.N., and anyone who vigorously advocates it will inevitably make enemies; but 3) this is hardly a reason not to advocate it. Turtle Bay is a crooked place. No U.S. ambassador can convert its self-serving bureaucrats and envoys of tyrants to standards of probity worthy of Sir Thomas More. What an ambassador can and should do is articulate correct principles as persuasively as possible, rather than sacrificing moral clarity for the sake of a superficial comity. And that is what Bolton did.

He made powerful arguments against the new U.N. Human Rights Commission, a body as morally bankrupt as its predecessor. He shone the spotlight on the atrocities in Darfur at a time when the world was inclined to forget them. He eloquently and persistently made the case against Iran’s nuclear program. He got the Security Council to pass a resolution sanctioning North Korea for its nuclear test, and put as much pressure as any man could on China actually to enforce it. All of this caps a long career of diplomatic achievements. On proliferation issues in particular, he has been visionary. The Proliferation Security Initiative — a vital tool for interdicting shipments of illicit arms — is his creation.

That he must now leave the U.N. is largely the fault of Lincoln Chafee, the liberal Rhode Island Republican who got a richly deserved electoral thrashing last month. He supported Bolton a year ago but refused to back him this time, effectively killing the nomination. Also at fault is outgoing committee chairman Richard Lugar, whose obsession with keeping his Democratic colleagues happy led him to delay a committee vote again and again and again; the wiser course would have been to put Chafee on the record before the Republican primary in which he faced a strong conservative challenger.

But blame must go above all to the Biden-led Democrats, who felt no qualms about undermining the implementation of U.S. foreign policy, a presidential domain. Their conduct with regard to the Bolton nomination has been even less justified than, for example, filibusters against judicial nominees. Those are objectionable too: but at least judgeships aren’t a branch of the executive. The Democrats have, moreover, hamstrung the administration at a time when the U.S. faces serious — potentially existential — threats from the Middle East and East Asia, and endeavors to counter these threats with sensitive and ongoing diplomatic efforts in which Bolton has played a crucial role.

On the other hand, Kim Jong Il and Mahmoud Ahmadinejad are probably delighted. Let no one deny that somebody’s interests have been served.