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“I think that the prospects of a future attack on the U.S. are almost a certainty. It could happen tomorrow, it could happen next week, it could happen next year, but they will keep trying. And we have to be prepared."

-- Then-Vice President Dick Cheney in a May 19, 2002 appearance on “FOX News Sunday.”

We once expected that life would be like this.

In the years after 9/11, many Americans believed that the new normal would include frequent, smaller-scale terrorist attacks. It was not if, but when.

Especially in Washington, every large gathering or major event even several years later was an occasion for twinges of worry – “How fast could I get the kids in the car if something happened?” “I’ve only got a quarter tank of gas. We’d never make it through the evacuation traffic jam.” “Who’s that weirdo shuffling around staring at his phone?”

It’s not that the Cherry Blossom Festival or even just a random Tuesday rush hour on the Metro were particularly high-profile targets. That was actually kind of the point. You could protect the Super Bowl or the Capitol during the State of the Union, but you couldn’t protect everything all the time and sooner or later, terrorists would move on to lower-profile, easier targets.

The operating assumption in those post-9/11 years was that we would have to live as Britons did during the worst of the IRA terror campaign or the Israelis do even to this day: always saddened but never surprised when the next attack came.

But the attacks didn’t come. At least not until Monday.

We don’t know what brand of terrorist bombed the Boston Marathon. There is a long menu of established sects from which to choose: Islamists, anarchists, racists, rebels from overseas. There is also the chance that this is the work of a sect of one, that like the epidemic of mass shootings in recent years, this is the product of one individual’s insanity, not an ideology.

The first modern mass murder at a school, the 1999 massacre in Littleton, Colo., killed 13 and spawned a years-long national debate, a top-grossing movie and a moment of cultural pause. The half-dozen since then have produced mostly momentary sorrow or, as with the most recent killings, a predictable and substantially unrelated political fight.

And had 9/11, or even the Oklahoma City bombing of 1995, been followed by a bombing every year or two, perhaps the result would have been similar when it came to terrorism on American soil. Perhaps it would have been a saddening normalcy.

That’s not to say that terrorists haven’t tried. Aside from the wannabes recruited by undercover agents into phony bomb plots, some, most notably the Times Square bomber and the underwear bomber, got close but had the wrong equipment or a poor plan. The only successful large-scale terrorist attack in the past dozen years was a brutally simple one involving a lone gunman opening fire on an Army unit bound for the war in Afghanistan, killing a dozen soldiers and one civilian.

But after so long with no bombings and the only news about terrorist plots being those that were foiled or bungled, Americans had again grown complacent. And that makes what happened in Boston more shocking and more horrible. There, on lovely Back Bay streets just a few blocks from the Public Garden where the Mallard family quacked for peanuts in “Make Way for Ducklings,” terror came back.

It would have surprised no one in 2003, but in 2013 it had again become unimaginable.

And Now, A Word From Charles

“Of course, it's nowhere near the scale of 9-11, but it's the first time [there has been a domestic bombing since then].  And I think that is sort of a historical echo that we're feeling, and it reminds us of how vulnerable we felt at the beginning of this whole decade of terror.  And even though we thought we had largely escaped, it is still out there.”

-- Charles Krauthammer on “Special Report with Bret Baier.”

Chris Stirewalt is digital politics editor for Fox News, and his POWER PLAY column appears Monday-Friday on FoxNews.com. Catch Chris Live online daily at 11:30amET  at  http:live.foxnews.com.