In retrospect, it seems oddly appropriate that Senator Lieberman’s primary defeat at the hands of Ned Lamont should have come during a month named after a Roman emperor. The chain of events that electoral setback sparked has now resulted in Mr. Lieberman effectively being crowned as Caesar of the Senate. The Democrats hold a majority of 51 to 49, but only as long as Mr. Lieberman caucuses with them, and whether he will continue to do so is a question that dangles over them like a Sword of Damocles.

That sword might just save the Democrats from themselves and make it possible for them to win future Senate majorities. He could help the Democrats adopt a strong stance on the war in the face of dovishness from their base in the blogosphere. They’ll be able to argue that they have no choice but to do the right thing, lest Mr. Lieberman bolt. This might keep Democrats from thinking that their victory was a vote for retreat in Iraq, when it is best viewed as a defeat for Republicans who had lost direction.

The Independent Democrat from Connecticut could also help on school vouchers. Mr. Lieberman abandoned his principled support for that reform to run for vice president with Albert Gore, only to see President Bush win on a pro-voucher platform. Mr. Lieberman could also lend support to the newly minted Senator Casey in carving out a space for pro-life Democrats, since he has always averred that abortion foes are not the kooks NARAL and the NOW make them out to be.

Democrats might even let Mr. Lieberman lead them toward tax cuts. He might not be the purest of supply siders, but he has been known to admit that tax cuts can be good for the economy. Although in recent years he has expressed opposition to Mr. Bush’s tax cuts, back in the 1990s, he joined Senator Hatch to sponsor a reduction in capital gains taxes. He has favored increasing the child tax credit and opposed the marriage penalty. It’s not exactly a tax-cut fervor, but it is an improvement over many Democrats.

For a view of how far off the rails Senate Democrats would be in danger of running without Mr. Lieberman’s sway, one need only look to the other side of the Capitol. Some observers had expected that a strategy centered on recruiting moderate candidates would lead to a more centrist majority. That may yet prove to be the case. But early signs are raising questions about the ability of a blue-dog freshman class in the House.

This is underscored by the leadership fight between Rep. Steny Hoyer, who is relatively stable on the war, and Rep. Jack Murtha, who has had what amounts to a breakdown in his credibility over Iraq. The speaker to be, Mrs. Pelosi, is preparing to elevate a singularly unfit congressman, Alcee Hastings, to the chairmanship of the Intelligence Committee, while demoting the more competent — and moderate — Jane Harman.

Moderate House Democrats have nowhere else to go. Not so Mr. Lieberman. The numbers speak to his power, and he needn’t fear the charge of being unfaithful, since it was the Democratic Party that was unfaithful to him. Mr. Lieberman has described himself as “liberated” and “unshackled,” as the New York Times noted yesterday in a wonderful dispatch by Mark Leibovich. It’s one of the ironies of this election that the worst thing the Democrats could have done — abandoning Mr. Lieberman in favor of Mr. Lamont — might turn out to be the best thing to happen to them this year.