Whether it would be a good idea for Senator McCain to choose Senator Lieberman as his running mate has been a topic of debate for several weeks now. Proponents of the idea say that Mr. Lieberman, an independent Democrat, would attract not only independents but the lunchpail blue-collar Democratic voters who have been averse to Senator Obama. It would signal that Mr. McCain aims to unite the country with his actions rather than just Obama-style rhetoric. It could help with Jewish voters in states such as Ohio, Pennsylvania, Florida, New Jersey, and maybe even New York and California.

Skeptics of the idea say that the choice wouldn’t help Mr. McCain, and might even hurt him, particularly in respect of the party’s conservative base, which is already dangerously lukewarm toward the Republican Party’s presumptive presidential nominee. Mr. Lieberman’s detractors also say that his age, 66, would only emphasize Mr. McCain’s own status as an elderly American, in contrast to Mr. Obama’s youthful vigor.

Let us just say that after Sunday night’s speech by Mr. Lieberman at the annual Commentary dinner, there is little doubt in our minds that the senator expelled by the Democrats two years ago in Connecticut would be a fabulous running mate for Mr. McCain. Concerns that he wouldn’t appeal to the conservative base? Mr. Lieberman pointedly referred to the New York Times as “a once-great newspaper” and said that the editor of National Review, William F. Buckley Jr., had been like an “older brother” to him. He noted that Buckley had endorsed him in the campaign when he first won election to the Senate, against a left-wing Republican, Lowell Weicker.

Mr. Lieberman spoke of how the Democratic Party had lost its way, from a party that was once “unhesitatingly and proudly pro-American,” to one that came under the sway of a philosophy that saw America as the aggressor. “There is now more isolationist sentiment in Democratic than in Republican ranks,” Mr. Lieberman said, deriding what he called the “McGovern-Carter blame-America worldview.” He attacked Senator Obama, saying that the “presumptive presidential nominee,” “has really not been willing to stand up to his party’s left on a single significant issue this far in his campaign.”

Mr. Lieberman criticized Mr. Obama’s promise to meet with President Ahmadinejad and with the North Korean dictator, Kim Jong Il, saying that Kennedy never met with Castro and Reagan never met with Ayatollah Khomenei. He pointed out that while Mr. Obama is courting the Iranians and the North Koreans, he is spurning our allies, opposing free trade agreements with South Korea and Colombia, and “pledging to abandon the democratically elected government in Baghdad.” He called President Bush’s speech in Jerusalem that Mr. Obama so heatedly objected to “magnificent.”

Our own view is that hard-line conservatives could make their peace with Mr. Lieberman as Mr. McCain’s running mate. Mr. Lieberman has cast some votes that are difficult for them. He’s repeatedly voted against bans on partial birth abortion, and he voted against confirming Justice Alito. On the other hand, there’s plenty there to like. He voted to confirm Justice Roberts, and in 1988 he told people he would have voted to confirm Robert Bork to the Supreme Court. His record on gun rights is better than one might expect; Connecticut is home to Colt, Ruger, and several other gun manufacturers.

Mr. Lieberman has also voted for school vouchers in the District of Columbia. He voted for NAFTA. Overlawyered.com has called him “one of the most prominent Democrats in support of tort reform.” He was out front in criticizing President Clinton during the Monica Lewinsky scandal — marking the moral issues, as we recall it, more clearly than anyone in the Senate — and has been outspoken against music, movies, and video games he says coarsen the culture.

From Mr. McCain’s point of view, the choice could actually make some sense. Everyone expects him to pick a young conservative governor from the Midwest like Timothy Pawlenty. Such a choice would likely be greeted by the press corps and the public with a collective yawn. But to have a candidate who ran as the Democratic vice presidential candidate in 2000 run as the Republican vice presidential candidate in 2008 — well, that has the capacity to confound the received wisdom. An MSNBC article pondering a McCain-Lieberman ticket noted that the two men had worked together in the Senate on climate change, judicial confirmations, campaign finance regulation, and the push to intervene militarily in Kosovo. It also noted that a former McCain aide, Marshall Wittmann, now works for Mr. Lieberman.

Mr. Lieberman has, in his 2006 general election victory over Ned Lamont, a demonstrated track record of success against a well-funded, blogosphere-backed anti-war candidate, something Mr. McCain might find useful if his rival in the general election is Mr. Obama. And Mr. Lieberman, having run for vice president in 2000, is fully vetted. Stuart Rothenberg of the Rothenberg Political Report called it a “near-perfect pick.”

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What any candidate, whether Mr. McCain’s age or younger, needs in a vice president is someone not to balance the ticket but to fill in as president in case fate intervenes. Were Mr. Lieberman to take over from Senator McCain, the voters would have every confidence that, on the key issues, their vote for Mr. Mr. McCain would be redeemed by a committed hawk in the war on Islamist terror, a patriotic American who believes in supporting freedom and human rights around the world, a free-trader, an experienced, veteran senator who can appeal to centrists and has a record of working across party lines to get legislation passed in Washington. A running mate will be one of the most important decisions Mr. McCain makes between now and the election. He will want to take the counsel of his political aides with caution, and give careful consideration to one of his closest friends in the Senate, someone who has been at his side since his endorsement on the eve of New Hampshire began a remarkable campaign turnaround that could well end at the White House.