It was just last month that the Democrats in the Senate were ganging up on the dean of Washington political reporters, David Broder, for suggesting that Senator Reid made a mistake by pronouncing that the war in Iraq was lost. Now it is Time magazine’s Joe Klein, who says Bush will be remembered as one of the worst presidents in history, who is in trouble with the left-wing bloggers. Mr. Klein’s crime is having written that maybe it wasn’t the brightest idea for the Democrats in Congress to vote to cut off funding for the troops and announce to the enemy the date of an American retreat in Iraq in the middle of a war. In a column we found linked at the center-right blog The Belmont Club, the Time columnist says he was greeted with “a fierce, bullying, often witless tone of intolerance that has overtaken the left-wing sector of the blogosphere.”

Says Mr. Klein, “Anyone who doesn’t move in lockstep with the most extreme voices is savaged and ridiculed — especially people like me who often agree with the liberal position but sometimes disagree and are therefore considered traitorously unreliable.” Mr. Klein writes that what happened to him is no big deal, but that the bloggers managed to sway Senators Clinton and Obama against voting for funding the war. The senators, he writes, “allowed themselves to be bullied into a more simplistic, more extreme position. Why? Partly because they fear the power of the bloggers to set the debate and raise money against them.”

There were activist factions in both the Republican and Democratic parties before the advent of the Internet. Talk radio, magazines, direct mail, and print and television advertisements were used to whip up popular sentiments long before blogs were. But if Messrs. Obama and Clinton run to cater to the bloggers, they may find themselves in the position of Ned Lamont, the peacenik Senate candidate of Greenwich, Connecticut, who won the Democratic primary but then lost the general election to an independent candidate who was more hawkish on the war. If Mr. Klein is trying to warn the Democrats of this, he isn’t a traitor, he’s trying to do them a favor. Whether the party’s candidates heed the warning will be one of the most important stories of the presidential campaign.