It seems to me that the differences between the wars in Vietnam and Iraq far outweigh the similarities. But it’s still useful to think of comparisons between the two. To date, there’s been a considerable difference between the two movements opposing the administration’s policy. On the one hand, public opinion has consolidated remarkably quickly against the Bush administration’s policies in Iraq, while for most of the 1960s, the anti-war position lacked majority popular support. On the other hand, the movement against the war in Iraq has had almost no policy impact, while the movement against the Vietnam War had a considerable impact in Washington, and at a relatively early stage.

Four years after Congress passed the Gulf of Tonkin Resolution, the only two senators to vote against it (Wayne Morse and Ernest Gruening) lost their re-election bids—partly because of their strongly anti-war positions. Public opinion polls from 1968 showed a majority either supporting LBJ’s policy or favoring an escalation of the conflict. Yet by this time, the Fulbright Hearings already had made challenging Cold War foreign policy respectable. In 1967, Congress passed a resolution sponsored by Mike Mansfield urging a negotiated settlement to the war. And congressional critics had scored important victories in curtailing Johnson’s military aid policy, as well as blocking the administration’s efforts to expand its commitment to Thailand. In short, the movement against the Vietnam War affected policy well before it ever enjoyed majority public support.

By this calculus, American troops should now be out of Iraq. Why aren’t they? Partially, of course, the explanation lies in the differences between the Congress of 1967 and that of 2005. As the United States has moved toward a quasi-parliamentary system, Congress has fewer and fewer members willing to challenge their party’s leadership on any issue of substantive importance.

But the character of the two anti-war movements also differs in ways that work against the current anti-war movement affecting policy. The Vietnam protest movement always had a radical contingent, which peaked in 1968. But from its start it also contained a powerful political arm. Sometimes the politicians were as radical as the grassroots protesters, as with Morse and Gruening in 1964. But, more often, the political arm took a more moderate position, allowing politicians who didn’t want to risk their careers to still challenge LBJ’s policies. By late 1967, William Fulbright, George McGovern, and Robert Kennedy (among others) could be identified as prominent politicians associated with an anti-war position.

Who, among today’s members of Congress, could be similarly identified? Political timidity might be one explanation for this reticence; the increasingly cookie-cutter nature of today’s politicians is another. But the nature of the public wing of the anti-war movement has also worked against politicians affiliating with it.

From its start, the conflict has generated intense opposition from forces on the extreme left of the American political spectrum—a stark contrast to Vietnam, where radical and more moderate anti-war voices developed simultaneously. As a result, the left extreme has been allowed to pass as the voice of the anti-war movement.

A reminder of this problem came in last weekend’s anti-war protest march in Washington. Earlier this week in Slate, Christopher Hitchens offered a savage and persuasive critique of the ideological agenda behind the march. Postings by some march supporters unintentionally reinforced Hitchens’ portrayal. According to Mazin Qumsiyeh, a Yale professor of genetics until December 2004 who in recent years served as faculty adviser to Yale’s Arab Students Organization, the protest march was “literally a sea of Palestinian flags (the most dominant flag at this demonstration).” Having the Palestinian flag as the dominant one at an anti-war demonstration is a political problem for the anti-war movement.

Quimsiyeh’s post came at the Yahoo group “Professors for Peace,” which describes itself as “an international network of educators committed to promoting non-violent solutions to global conflicts and to countering racism and anti-immigrant aggression,” since “as educators, we recognize our responsibility to foster constructive dialogue in our classrooms, on our campuses, and in local, national, and international forums.”

The former Yale professor offered some other fantastic insights, including a claim that Israeli security agents trained “US troops in methods of urban warfare’ (read collective punishment and other war crimes)” and “are now in New Orleans getting taxpayer money to occupy our US cities.” Qumsiyeh added that Democratic members of Congress boycotted the anti-war rally not because of its extremist message but because AIPAC “put out the word that any member of Congress who appeared at the protest, where some speakers were to represent pro-Palestinian views, would face the political wrath of AIPAC,” a message allegedly conveyed by Barney Frank.

With this kind of agenda, it’s no surprise that Georgia congresswoman Cynthia McKinney, known for indulging occasional anti-semitic conspiracy theories, was one of only three members of the House to address the rally. (No senators did.) The close linkage between the movement against the Iraq war and other issues (especially hostility to Israel, but also opposition to the war in Afghanistan and the Patriot Act ) that enjoy widespread popular support helps explain why the only politicians we see taking strongly anti-war positions are those like Cynthia McKinney.