Immigration is one of our nation's festering wounds. It has been so for years -- no matter the locale, no matter which political party is in charge, no matter how much the attitudes of our citizens change. Always simmering in the best of times, our fight over this issue can erupt ferociously with a single act as its touchstone.

Now we're reeling from the senseless killing of a woman in San Francisco by a Mexican man in the country illegally. Francisco Sanchez, who has admitted shooting her last week, had been deported five times. He had seven felony convictions, four involving drug charges. The horrible incident, now part of Donald Trump's rhetoric about what kind of people cross the border illegally, has centered the debate on San Francisco's status as a so-called sanctuary city. It's one of dozens of municipalities that -- whether by law or practice -- have chosen to not cooperate fully with federal immigration authorities on the criteria for locking up certain immigrants while deportation proceedings take place. Local officials are concerned aggressive immigration enforcement deters law-abiding immigrants from cooperating with authorities.

The furor over Kathryn Steinle's slaying, while understandable, has mostly missed the broader point that our nation has repeatedly failed to address comprehensive immigration reform. Congress simply refuses to do it, and action always is on hold until after the next election. And make no mistake: The lack or reform led to Sanchez slipping through the cracks.

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President George W. Bush pushed reforms that died in 2007. The Senate's 2013 bipartisan bill languished in the House of Representatives. Executive actions by President Barack Obama last fall have been blocked temporarily in court. Now Steinle's slaying is being used by haters to justify anti-immigrant sentiments such as those of Trump, who has smeared Mexican immigrants here illegally. Such raw divisiveness is only destructive.

It's important to note Sanchez is the exception, not the rule. And that there is no question he should not have been in this country. U.S. Immigration and Customs Enforcement and the San Francisco sheriff's office are engaged in furious finger-pointing over who's at fault.

Long Island is not immune from immigration tensions. A Brentwood man recently reached a settlement with the federal government over the 2011 detention and deportation of his then-4-year-old daughter -- a U.S. citizen. Last week, a Guatemalan immigrant bicycling home from work was beaten unconscious by three men in Farmingville in what's being termed a hate crime -- an eerie echo of the 2001 near-deadly beating of two Mexican day laborers in Farmingville, and the 2008 slaying in Patchogue of Ecuadorean immigrant Marcelo Lucero.

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Immigration across our Southern border has slowed. Frustrated with Congress' failure to act, the Obama administration reportedly reversed its policy of mass deportation and is now targeting for deportation three groups -- criminals, terrorism threats and recent arrivals.

All of this unfortunately never gets us any closer to the tough discussion about reforming our broken immigration system. All of us need that, whether we're here legally or not.