The last time that Democratic primary voters turned out a nationally-known U.S. Senator because they did not like where he stood on an issue of war and peace was in 1970, when Texas Democrats rejected anti-war incumbent Ralph Yarborough and replaced him with Lloyd Bentsen, a former congressman who favored taking a tougher line against the Vietcong in Vietnam and against student protesters on the campuses of the United States.

The Texas result was big news nationally, and it played a significant part in the decision of the Nixon White House to try and stir up a “silent majority” backlash to congressional liberals in that fall’s Senate races.

Thirty-six years later, in a very different state, Democratic primary voters may avenge Yarborough’s loss and set in motion a backlash of another character altogether.

If anti-Iraq War challenger Ned Lamont defeats pro-war incumbent Joe Lieberman in today’s contest for the Democratic Senate nod in Connecticut, and if Democrats in Washington finally figure our that no message energizes their base so much as the “Bring the Troops Home” signal that Lamont has sent, then the 2006 election could yet be the referendum on George W. Bush’s misguided policies that Democrats denied voters in 2002 and 2004.

There were a lot of “ifs” and “coulds” in that previous paragraph. Here’s why: Though Lamont took a poll lead several weeks ago, there were some indications in the final days of the race that Lieberman was making something of a comeback. A Quinnipiac poll released yesterday had Lamont at 51 percent and Lieberman at 45 percent – suggesting a closer contest than the one seen in polls from last week, which had Lamont up by 10 to 13 points.

Could Lieberman still win this thing? It’s not beyond the realm of possibility. Though his reelection campaign has been pathetic, and though he is dramatically out of touch with Democrats on the war issue, the incumbent retains strong name recognition, he has most of the major endorsements from interest groups and newspapers in the state, and he has spent a lot of money on a bitterly negative television advertising campaign against Lamont.

It is the prospect that Lieberman could have a little more going for him than has seemed to be the case through much of the primary fight that has the Lamont campaign working harder than ever today. The narrowing of the polls is likely to bump turnout, perhaps to an unprecedented 45 or 50 percent of the potential primary electorate. The best bet is that this will help Lamont, but the uncertainty about who all these new voters might be – in a state where it is relatively easy for Republicans and independents to reregister as Democrats and participate in the primary – will have everyone on edge until the results are in this evening.

Even if Lamont wins, there is still that bigger “if.” Will Democrats in Washington get the message that the war is the issue that gets voters to the polls and that, ultimately, poses a threat to stay-the-course incumbents of both parties? The answer to that question has a lot to do with the size of the margin in Connecticut.

If Lamont wins narrowly – say, by under four points – Lieberman will claim that Democrats are just about evenly divided and plunge into a third-party challenge to the Democratic nominee as the candidate of his newly-created “Connecticut for Lieberman” party.

On the other hand, if Lamont secures a decisive victory with a margin of ten points of more, then the pressure on Lieberman to accept the result will intensify. It will become difficult for the incumbent to hold onto those endorsements from groups such as the AFL-CIO, Planned Parenthood and the League of Conservation Voters. And the senator might either forego a fall race or mount a titular campaign that will ultimately be a sad footnote to a lamentable career.

If Lieberman has to hang it up tonight or in the next few days, Democratic Party leaders in Washington are likely – because of the intensity of interest in this contest – to be forced by a suddenly engaged press corps to speak with a measure of clarity about where they stand on the war. Chances are that they will try to firm up a message that on the eve of the primary was still better defined as a “whine” than a muscular challenge to Bush and the neoconservatives.

The prospect that the Connecticut primary could be about more than one state’s Senate nomination is what will make tonight a rare moment in American politics. It has been a long time since a Democratic Senate primary shifted the direction of national politics. If this one does, and if it pushes the party in the direction of the anti-war position embraced by most Americans at this point, then this will be a historic day – the day when, after far too long, our politics again became meaningful.