The website Politico — which covers politics, naturally enough — reported this week about an escalation in “opposition research” that should concern Americans of all political persuasions.

For those who aren’t familiar with what campaign strategists call “oppo,” it usually involves researching an opponent’s public history to dig up videos, statements or other public facts that can be used to cast the target’s present-day qualifications into doubt.

Politics being a contact sport, there’s nothing unethical about those activities, and voters can be responsible for sorting out the claims they produce, just as they are for any other political ad.

But until recently, unless something in a candidate’s private life entered the public sphere on its own, there was a line drawn between the personal and political that was very rarely crossed.

That seems to be behind us now, however. Candidates are used to having opponents’ representatives film their speeches and other public actions, hoping to find a “gaffe” or other slipup that would provide fodder for an attack ad.

But according to a Politico report titled “GOP unnerved by Democrats’ candid camera tactics,” cameramen have been lurking around several Republican congressional candidates’ private homes and posting the videos, with addresses, on the Internet.

The purpose appears to be to show that these candidates live in nice, well-kept houses, and thus are (in the minds of their opponents) unable to sympathize with the poor.

But in order to judge that fully, voters would also have to see the homes that the Democrats live in — and if this practice continues, there is little doubt that they soon will.

Not only is this a scandalous invasion of privacy, but we have already had one member of Congress, Gabrielle Giffords, shot by a deranged stalker. Enabling others to track potential targets to their homes puts not only the candidates in danger, but their families as well.

This unethical — and dangerous — practice should stop now. And if it does not, it offers adequate reason by itself to vote against those who permit it to be done in their names.