The New York Times is endorsing Ned Lamont in his primary race against Joe Lieberman.

Earlier this year, Senator Joseph Lieberman's seat seemed so secure that -- legend has it -- some people at the Republican nominating convention in Connecticut started making bleating noises when the party picked a presumed sacrificial lamb to run against the three-term senator, who has been a fixture in Connecticut politics for more than 35 years.

But Mr. Lieberman is now in a tough Democratic primary against a little-known challenger, Ned Lamont. The race has taken on a national character. Mr. Lieberman's friends see it as an attempt by hysterical antiwar bloggers to oust a giant of the Senate for the crime of bipartisanship. Lamont backers -- most of whom seem more passionate about being Lieberman opponents -- say that as one of the staunchest supporters of the Iraq war, Mr. Lieberman has betrayed his party by cozying up to President Bush.

This primary would never have happened absent Iraq. It's true that Mr. Lieberman has fallen in love with his image as the nation's moral compass. But if pomposity were a disqualification, the Senate would never be able to call a quorum. He has voted with his party in opposing the destructive Bush tax cuts, and despite some unappealing rhetoric in the Terri Schiavo case, he has strongly supported a woman's right to choose. He has been one of the Senate's most creative thinkers about the environment and energy conservation.

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But this race is not about résumés. The United States is at a critical point in its history, and Mr. Lieberman has chosen a controversial role to play. The voters in Connecticut will have to judge whether it is the right one.

As Mr. Lieberman sees it, this is a fight for the soul of the Democratic Party -- his moderate fair-mindedness against a partisan radicalism that alienates most Americans. "What kind of Democratic Party are we going to have?" he asked in an interview with New York magazine. "You've got to agree 100 percent, or you're not a good Democrat?"

That's far from the issue. Mr. Lieberman is not just a senator who works well with members of the other party. And there is a reason that while other Democrats supported the war, he has become the only target. In his effort to appear above the partisan fray, he has become one of the Bush administration's most useful allies as the president tries to turn the war on terror into an excuse for radical changes in how this country operates.

Citing national security, Mr. Bush continually tries to undermine restraints on the executive branch: the system of checks and balances, international accords on the treatment of prisoners, the nation's longtime principles of justice. His administration has depicted any questions or criticism of his policies as giving aid and comfort to the terrorists. And Mr. Lieberman has helped that effort. He once denounced Democrats who were "more focused on how President Bush took America into the war in Iraq" than on supporting the war's progress.

At this moment, with a Republican president intent on drastically expanding his powers with the support of the Republican House and Senate, it is critical that the minority party serve as a responsible, but vigorous, watchdog. That does not require shrillness or absolutism. But this is no time for a man with Mr. Lieberman's ability to command Republicans' attention to become their enabler, and embrace a role as the president's defender.

Update: Hermie made an excellent observation: "Funny how only 6 years ago the NYT proclaimed that Lieberman was qualified to become the Vice President of the United States; yet now he is not even worthy of being a US Senator."