It’s almost enough to make you feel sorry for the Democratic presidential candidates. Just as they’re settling into their game plans, one inconvenient truth after another emerges to disrupt them. And that doesn’t even include Al Gore’s weather forecasts.

Last week was especially nettlesome. It started with GOP front-runner Rudy Giuliani laying down the marker that America would be safer with a Republican president, a surprise attack that put the Dems’ Gang of Eight on the defensive. Then in quick succession came former CIA Director George Tenet’s warning of likely al-Qaida attacks in the United States and a report that Saudi Arabia had arrested 172 militants who were plotting to blow up oil installations in the desert kingdom.

The cumulative effect was to remind the nation that the war on terror, or whatever it’s called these days, is far from over. That reminder served as a warning to the candidates that wooing liberal primary voters with too much peace talk could put the party’s nominee at odds with swing voters in next year’s general election.

Even attacking President Bush on Iraq offers no political haven. Just as Dems in Congress finally pushed through a unified bill requiring Bush to start bringing the troops home, our commander in Iraq, Gen. David Petraeus, was in Washington warning that a pullback would mean even more violence. In response to some Democrats who say Iraq is so bad our actions don’t matter much, Petraeus laid down his own marker: “It can get much, much worse,” he said.

Sen. Hillary Clinton expressed the squeeze she was feeling, saying, “We don’t want Democrats being blamed for our troops not being well-equipped” even though they want them home.

Campaigns, of course, are never smooth and easy. Surprises don’t come only in October. An event can come out of nowhere and instantly change the dynamics, making a mess out of assumptions and strategies. The position that looked smart Monday can create a new vulnerability Tuesday.

For Democrats, nothing has the power to disrupt politics like terrorism. The belief that Bush was better at fighting it cost John Kerry the election he should have won in 2004. Although public disgust with Bush’s handling of Iraq won Dems both houses of Congress last year, the ability of genuine threats of terrorism to create a new sense of insecurity among voters remains just a headline away.

The subject even caused a stir in the sober first debate on Thursday. Moderator Brian Williams’ surprising question about a hypothetical attack on two U.S. cities forced the candidates to snap out of their bring-the-troops-home, Bush-bashing party and play commander in chief. Given how anti-war activists are pulling the party leftward, the question seemed to catch nearly all the candidates off guard at first. Sen. Barack Obama recovered to issue a strong rebuke to the peaceniks on the stage, but it’s clearly not a big subject in any of their campaign playbooks.

But reality has a way of intruding. Coincidentally, Tenet, in a new book devoted mostly to trying to resurrect his reputation and trash Vice President Cheney’s, also raises the possibility of new attacks. He writes that he is puzzled that al-Qaida has not unleashed “suicide bombers to cause chaos in a half-dozen American shopping malls on any given day.”

He goes on: “I do know of one thing in my gut. Al-Qaeda is here and waiting.”

And now Democrats know it, too. Whatever else happens, they can’t say they weren’t warned.