Then as now, the incumbents belittled the influence of the insurgents. John Roche, serving in the Lyndon Johnson White House, dismissed critics of the Vietnam War as a "bunch of Upper West Side Jacobins." (The journalist to whom he issued the dismissal, Jimmy Breslin, unfamiliar with French history, transcribed the word as "jackal bins." The next day, the story goes, half the Upper West Side found itself wondering, "What the hell is a jackal bin?")

Now as then, however, the insurgents are slowly shifting the incumbents. Just as the post-1968 Democratic Party came to look more like Eugene McCarthy's movement than Hubert Humphrey's coalition, so today's liberal FPC is gradually adopting not only many of the actual views, but much of the tone, style and manner of the left blogosphere.

FEW PRESIDENTIAL candidates have drawn more support from the liberal FPC than Barack Obama. Obama has been endorsed by former National Security Advisor Zbigniew Brzezinski and advised by Harvard professor Samantha Power, Clinton counter-terrorism czar Richard Clarke and even George W. Bush's former NSC Senior Director for the Middle East, Bruce Riedel. Compared to Obama's, Hillary Clinton's foreign-policy team looks a little like a gala performance in Branson, Missouri: all the names you remember from decades ago. ("Madeleine Albright is still fabulous!")

And yet as Obama has struggled to come from behind in Iowa and New Hampshire, this once-irenic candidate now hurls accusations with the brio of a blogger on the Daily Kos.

Here is Obama on the Senate's Kyl-Lieberman amendment, a non-binding "sense of the Senate" resolution urging the administration to designate Iran's Revolutionary Guards as a terrorist organization, a resolution that won the votes of a majority of Senate Democrats:

Why is this amendment so dangerous? Because George Bush and Dick Cheney could use this language to justify keeping our troops in Iraq as long as they can point to a threat from Iran. And because they could use this language to justify an attack on Iran as a part of the ongoing war in Iraq.

Three years ago, Barack Obama was willing to contemplate outright war against Iran. Running for Senate in 2004, he told interviewers that he regarded an Iranian nuclear bomb as a "worse" outcome than air strikes against Iran. Now, though, he has been pushed toward the blogger view that war is not to be contemplated, period. And he has adopted the blogger habit of attributing deceit and bad faith to anyone who disagrees with him-or even to anyone who agrees today with the positions he used to hold yesterday.

THE BLOGOSPHERE exerts its influence in two ways-one as hard as cash, the other as whispery as a mirage.

In two consecutive presidential election cycles, the Internet has proven itself the most effective fundraising technology since the advent of direct mail. The last cycle's Internet darling, Howard Dean, raised money at the fastest pace ever seen: a million dollars a week, almost all of it in very small gifts, in the second two quarters of 2003. In the first quarter of 2007, Barack Obama matched Hillary Clinton's astonishing fundraising totals by tapping almost twice as many donors: 100,000 against her 50,000. On November 5, 2007, Ron Paul used the Internet to raise the largest one-day total in the history of political fundraising, $4.5 million.

Any medium that lucrative is bound to hold the attention of politicians. And bloggers look very much like the custodians of the political Internet.

The more whispery power comes from the strange echo-chamber effect of the Internet. The blogosphere links people all over the planet. It can generate volumes of comments and email that feel like a tidal wave to those accustomed to the milder responsiveness of the print medium. When I worked on the opinion page of The Wall Street Journal, then the largest circulation newspaper in America, a very provocative article might have elicited as many as a hundred letters to the editor. Today, an exciting post on a major blog can generate thousands of posted comments and emails. Few people possess the internal fortitude to stand up to a seeming barrage like this. (Joe Klein, whom I cited above as a special target of the left blogosphere, has retreated under pressure into something very like the party-line liberalism he once disdained.)

For those who participate in it, the blogosphere takes on the scale and reality of an alternative world-a world whose controversies and feuds are so absorbing, whose alliances and enmities burn with so much passion, that only the most level-headed of the participants ever seem to remember that somewhere between 97 and 98 percent of American voters have never looked at a blog in their lives.

THE VIRTUAL-REALITY quality of the blogosphere accounts for one of the most puzzling traits of the left-wing bloggers: their ability to believe simultaneously in a) the supreme importance of winning elections for Democrats and b) the supreme importance of moving the Democratic Party to the left-"Running as a progressive will lead to victory", predicts Matt Stoller, one of the left blogosphere's leading voices-in flat contradiction of four decades of post-1968 experience that running as a progressive leads Democrats only to disaster.

But if everyday progressives sustain themselves in a hothouse atmosphere of positive feedback-if any murmur of doubt or skepticism is met with a barrage of abuse-if all the human instincts toward tribe and clan are harnessed to a partisan cause, then such things as historical experience or cautionary opinion polls can easily be shrugged aside.

Or anyway, shrugged aside up to the point where reality becomes undeniable.

And perhaps it is the power of undeniably adverse reality that prevents the right blogosphere from using the kind of force and power on foreign policy that its left counterpart exerts.

Any Republican attuned in any way to current events knows that the party faces grave difficulties and dangers going into 2008. Republicans cannot afford to indulge the illusions with which progressives can entertain themselves this cycle. (I should say: most Republicans. There is the countervailing example of the Ron Paul fanatics, who have convinced themselves that their man can sweep to victory on a platform that last won a presidential election in 1836.) For this reason, the Republican field is led by two men, who each in their way offer a new centrism.

The conservative blogosphere scored its last great triumph in 2005, when it led the rebellion that forced the withdrawal of the Supreme Court nomination of Harriet Miers. Its next great cause-exposing the pervasive faking of images in the 2006 Israeli-Hizballah war and the probable forgery of the video purporting to show the shooting of Muhammad al-Dura-has not achieved anything like such success. One Reuters photographer was caught in the act and forced to resign, but the creation of doctored images, like the al-Dura video, continues to command wide acceptance even in the West.

THE BLOGOSPHERE is a place of anger and enthusiasm. In 2007, Republicans are less angry and enthusiastic than Democrats, and so their share of the territory is both smaller and less energetic. That will not always remain true. If Democrats do less well in 2008 than they now anticipate, some in the party will blame the blogosphere for pushing the party too far to the anti-war extreme. Alternatively, if Democrats capture the White House, the left blogosphere may well lose the energy of opposition, as conservative talk radio did after Bill Clinton left office.

Yet there is reason to think that the gravitational effect exerted on the liberal FPC by the left blogosphere will extend across party lines-and beyond the current political cycle.

Through the twentieth century, the management of American foreign policy has time and again been snatched away from the mandarins who regard themselves as its proper custodians. A populist eruption thwarted the hopes of the liberals around Woodrow Wilson in 1919-20. After the defeat of the Versailles Treaty, public interest waned-and Republican presidents were left free to conduct "dollar diplomacy." Another populist moment deterred Franklin Roosevelt from responding to the rise of Hitler in the 1930s, until Pearl Harbor put the experts back in control again. There they stayed until Korea and Joe McCarthy dethroned them-and back onto the throne they scrambled again during the "thinking the unthinkable" years from 1955 to 1965. And so it has continued into our own time. The frustrations over Iraq have triggered a reaction very similar to that generated by the stalemate in Korea, creating an audience for similar kinds of explanations-with "neocons" this time taking the part once assigned to the "striped-pants boys" in the State Department, and the high-toned Professors Stephen M. Walt and John J. Mearsheimer reinterpreting the role formerly played by William Knowland and Senator McCarthy.

Yet on each round of the cycle, the spread of education and the improvement of communications have raised the level of debate. The populist protesters of 2007 are far more informed and far more sophisticated than their predecessors of 1973, who were in turn a major improvement over those of 1950, 1935 and 1920. And the foreign-policy community that guided U.S. foreign affairs in the 1990s was a much larger and more diverse group than the corresponding elites that wielded power in the quiet days of the 1950s, who were in turn a less cloistered club than that of the 1920s.