Political handlers caution candidates against speaking off-the-cuff. Undisciplined candidates, they say, commit gaffes.

This seems reasonable, but some of the most harmful gaffes of late weren’t the result of unexpurgated comments, but rather, of recycled or rehearsed comments being used one too many times.

Just ask Mitt Romney, who was stunned to learn that saying he was “not concerned about the very poor” caused more than minor contretemps, After all, as he explained, he had “said something that is similar” for a long time.

In politics, selective outrage and mixed signals are often the norm.

Less than 24 hours before telling Andrea Mitchell a joke about gals putting aspirin between their knees (the best contraception!), Rick Santorum’s top financial backer delivered similar remarks at a conservative dinner. The audience laughed, no doubt, reinforcing the notion that the joke might work elsewhere. It didn’t.

And who could forget the huge uproar over Newt Gingrich’s remarks implying Rep. Paul Ryan’s budget was “right wing social engineering”?

The controversial line — which dominated headlines for days — was likely borrowed from Ryan’s old boss (and Newt’s old friend), New York Rep. Jack Kemp, who, in 1990, wrote: “Conservative social engineering is every bit as presumptuous as liberal social engineering.” I don’t recall anyone criticizing Kemp — who was generally viewed as a solid fiscal conservative — for the line.

So why are some lines passable one day, but utterly outrageous the next?

Some of it is probably luck. Sometimes controversial lines go unnoticed by the press. This lulls candidates into a false sense of security — or even emboldens them to add them to their stump speeches. And then, they say it at the wrong place, in the wrong way, in front of the wrong reporter — and it blows up.)

Of course, sometimes there is orchestrated outrage. Rush Limbaugh has said many controversial things (by design) over the years. But his enemies (having found a sympathetic spokesvictim in Sandra Fluke) pounced on a recent line — launching a political campaign to target his advertisers.

Likewise, Pat Buchanan has written and said many controversial things over the years, but there a campaign to get him off MSNBC finally worked. And Don Imus, too, had said many crude and outrageous things which crossed the line of good taste and appropriateness — before someone decided to be outraged. (He must have been surprised when the shoe finally dropped.)

In other cases, it’s a matter of context or timing. We care more about what a presidential candidate says than what an ex-politician says on the lecture circuit. Gingrich’s line about social engineering came from a presidential candidate. What is more, it occurred right after a conservative rising star put his neck on the line proposing a plan for serious entitlement reform.

When it comes to whether or not a comment is deemed acceptable or outrageous, the public is often capricious. One day something is a throwaway line, the next day, it’s a serious gaffe. There is often no rhyme or reason.

So the ultimate lesson is this: Just because a line worked once — just because it elicited only yawns once — doesn’t mean that it won’t spark controversy later. Some of the aforementioned people went to the well, as they say, one too many times.