Presidents, arrogant men, lie. And yet the media, loath to undermine the authority of the commander in chief, trusts them. Today's congressional war critics have to be ready for that. They have to do what Congress immediately did next, in 1970: It grasped the nettle, at the president's moment of maximum vulnerability, and turned public opinion radically against the war, and threw the president far, far back on his heels.

Immediately after the Cambodian invasion Senate doves rolled out three coordinated bills. (Each had bipartisan sponsorship; those were different days.) John Sherman Cooper, R-Ken., and Frank Church, D-Idaho, proposed banning funds for extending the war into Cambodia and Laos. Another bipartisan coalition drafted a repeal of the Gulf of Tonkin resolution, the congressional authorization for war that had passed 98 to 2 in 1964. George McGovern, D-S.D., and Mark Hatfield, R-Ore., were in charge of the granddaddy of them all: an amendment requiring the president to either go to Congress for a declaration of war or end the war, by Dec. 31, 1970. Walter Shapiro wrote that a "skittish" Congress made sure its antiwar legislation had "loopholes" to permit the president to take action to protect U.S. troops in the field" -- which means no genuine congressional exit mandate at all. But McGovern-Hatfield had no such "loopholes." (Of course, McGovern Hatfield didn't pass, and thus wasn't subject to the arduous political negotiating process that might have added them.) It was four sentences long, and said: Without a declaration of war, Congress would appropriate no money for Vietnam other than "to pay costs relating to the withdrawal of all U.S. forces, to the termination of United States military operations ... to the arrangement for exchanges of prisoners of war," and to "food and other non-military supplies and services" for the Vietnamese.

Radical stuff. Far more radical than today's timid congressional critics are interested in going. But what today's timid congressmen must understand is that the dare paid off handsomely. With McGovern-Hatfield holding down the left flank, the moderate-seeming Cooper-Church passed out of the Foreign Relations Committee almost immediately. Was the president on the defensive? And how. His people rushed out a substitute "to make clear that the Senate wants us out of Cambodia as soon as possible." Two of the most hawkish and powerful Southern Democrats, Fritz Hollings and Eugene Talmadge, announced they were sick of handing blank checks to the president. A tide had turned, decisively. By the time Cooper-Church passed the Senate overwhelmingly on June 30, the troops were gone from Cambodia -- an experiment in expanding the war that the president didn't dare repeat. Congress stopped that surge. It did it by striking fast -- and hard -- when the iron was hottest. In so doing, it moved the ball of public opinion very far down the field. By August, a strong plurality of Americans supported the McGovern-Hatfield "end the war" bill, 44 to 35 percent.

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McGovern-Hatfield did not pass in 1970. But the campaign for it helped make 1971 President Nixon's worst political year (until, that is, Congress' bold action starting in 1973 to investigate Watergate). By that January, 73 percent of Americans supported the reintroduced McGovern-Hatfield amendment. John Stennis, D-Miss., Nixon's most important congressional supporter, now announced he "totally rejected the concept ... that the President has certain powers as Commander in Chief which enable him to extensively commit major forces to combat without Congressional consent." In April the six leading Democratic presidential contenders went on TV and, one by one, called for the president to set a date for withdrawal. (One of them, future neoconservative hero Sen. Henry "Scoop" Jackson, differed only in that he said Nixon should not announce the date publicly.)

This was a marvelous offensive move: It threw the responsibility for the war where the commander in chief claimed it belonged -- with himself -- and framed subsequent congressional attempts to set a date a reaction to presidential inaction and the carnage it brought. When the second McGovern-Hatfield amendment went down 55-42 in June, it once more established a left flank -- allowing Majority Leader Mike Mansfield to pass a softer amendment to require withdrawal nine months after all American prisoners of war were released. Senate doves, having dared the fight, were doing quite well in this game of inches.

During the first administration of Franklin Delano Roosevelt (or so goes a story now making the rounds of American progressives), the president met with a group of citizens who urged him to seize the moment. Surely it was time for serious reforms: The Depression made it impossible to continue with business as usual. Just what measures the visitors to the Oval Office proposed — well, that is not clear, at least from the versions I have heard. Perhaps they wanted laws to regulate banking, or to protect the right of labor unions to organize, or to provide income help for the aged. Maybe all of the above.

The president listened with interest and evident sympathy. As the meeting drew to a close, Roosevelt thanked his guests, expressing agreement with all they had suggested. “So now,” he told them on their way out the door, “go out there and make me do it.”

This is less a historical narrative, strictly speaking, than an edifying tale. Its lesson is simple. Even with wise and trustworthy leadership holding power — perhaps especially then — you must be ready to apply pressure from below. (The moral here is not especially partisan, by the way. One can easily imagine conservative activists spurring one another on with more or less the same story, with Ronald Reagan assuming the star role.)

The idea that mass movements might constitute a fourth sector of the party – with the Christian Right, for example, being a component of the Republican “party in the street” – might seem self-evident in some ways. But not so for political scientists, it seems. “We met a lot of resistance to the idea of the ‘party in the street,’” Heaney told me ... Speaking of the antiwar protests as manifestations of the Democratic “party in the street” will also meet resistance from many activists. (A catchphrase of the hard left is that the Democratic Party is “the graveyard of mass movements.”) And according to their own surveys, Heaney and Rojas find that just over one fifth of demonstrators see themselves as clearly outside its ranks.

But that still leaves the majority of antiwar activists as either identifying themselves as Democrats or at least willing to vote for the party. “Like it or not,” write Heaney and Rojas, “their moral and political struggles are within or against the Democratic Party; it actions and inactions construct opportunities for and barriers to the achievement of their issue-specific policy goals.” (Though Heaney and Rojas don’t quote Richard Hofstadter, their analysis implicitly accepts the historian’s famous aphorism that American third parties “are like bees: they sting once and die.”)

“We do not claim,” they take care to note, “that the party in the street has equal standing with the party in government, the party in the electorate, or the party as organization. We are not asserting that the formal party organization is coordinating these activities. The party in the street lacks the stability possessed by other parts of the party because it is not supported by enduring institutions. Furthermore, it is small relative to other parts of the party and at times may be virtually nonexistent.”

As Heaney elaborated when we met, a great deal of the organizing work of the antiwar “party” is conducted by e-mail – a situation that makes it much easier for groups with a small staff to reach a large audience. But that also makes for somewhat shallow or episodic involvement in the movement on the part of many participants. An important area for study by political scientists might be the relationship between the emerging zone of activist organizations and the informal networks of campaign consultants, lobbyists, financial contributors, and activists” shaping the agenda of other sectors of political parties. “If they remain well organized and attract enthusiastic young activists,” write Rojas and Heaney, “then the mainstream political party is unable to ignore them for long.”