FOR EVERY ACTION, there is an equal and opposite reaction. At least in physics. In politics, however, the equation isn’t always symmetrical. A mild push might invite a whopping Sunday punch. Likewise, an unbridled onslaught might go completely unanswered.

So what about this nationwide chain reaction of immigrant demonstrations, school walkouts, a freeway blockade, and Saturday’s historic rally that brought hundreds of thousands into the streets of Los Angeles? Will this feisty and largely unanticipated show of force by an “illegal” underclass — replete with flapping Mexican flags — provoke some ferocious, crushing backlash of xenophobia and reprisal? Are we in for an amped-up repeat of 1994, when a much smaller downtown demo of Latinos helped fuel, a few weeks later, a revanchist white-voter turnout in favor of the rights-stealing Proposition 187?

This nightmare scenario is what some analysts are predicting. Problem is, they’ve got it backward. The feared nativist backlash has been in full motion now for some time — long before the humongous immigrant demonstration last weekend. The groveling media suck-up to the minuscule Minutemen show (hundreds of journalists shamelessly traipsing behind a few score vigilantes) a year ago established a twisted and ugly frame for a national debate that had been delayed way too long. The Lou Dobbsian jibber-jabber about “broken borders” reached its crescendo last Christmas, when the House passed the outrageous Sensenbrenner bill that would deem all so-called illegal aliens — and their employers — felons. (Undocumented workers currently are in violation of civil, not criminal, codes.)

Why should anyone feign surprise when an entire population that cleans our offices, cuts our lawns, serves our food, makes our beds, tends to our children, and pays taxes but gets no refunds, finds it expedient to mobilize politically against its wholesale criminalization? It’s asking a lot, don’t you think, for workers to remain silent and impassive as their arrest and deportation are actively being contemplated in Congress? The only surprise is that it has taken this long to materialize.

Our contemporary Cassandras, those who in 1962 would have lectured Dr. King that he was only stirring up Mr. Charlie by pushing his Negroes too far too fast, might recall that the white backlash of 1994 was immediately followed by a counterbacklash. An enraged and energized Latino constituency accelerated its entrance into citizenship and onto the voter rolls, and within four years it steamrollered the California GOP — a flattening from which state Republicans have still not recovered.

So while the grumbling Archie Bunkers might get their ya-yas all worked up by the Mexican flags unfurled in Saturday’s demo, the smarter among Republican strategists look upon the size of those protests with some pause and trepidation (if not with a calculator in hand). Many of those in the rally were legal, or have legal relatives, or, if illegal, might soon be legal. And they could hardly be counted on to vote for a party that would continue denying their existence. There’s a reason why George W. Bush isn’t replicating the despicable demagogy of Pete Wilson. At least he, if not all of his fellow Republicans, has assimilated the lessons of Prop. 187.

I don’t think that the sudden upsurge in marches and demos in any direct way encouraged a handful of key Republican senators to join with Democrats on Monday in approving a sweeping and liberalized comprehensive immigration-reform measure (which still faces an uphill battle on the full Senate floor). What’s astounding is that the protests weren’t used as an excuse to not do so. How could they when, at virtually the same moment the protesters overflowed downtown, the president’s own radio address broadly endorsed the two principal demands of the demonstrators: expanded legal immigration and some channel or another through which the 12 million illegals already here can come into legal status.

THE ONLY ARGUMENT we — as a nation of immigrants — can make against the current migratory wave is that our grandparents and parents came here legally, so why don’t Jose and Maria do the same? Well, the America of 2006 is not the America that my family came to in 1915 (and when they came, they also pushed aside better-paid, longer-term residents and citizens). Our work force is vastly older and immensely better educated and skilled than even 50 years ago. The industrial revolution, which was roaring ahead a century ago, has given way, unfortunately, to a service economy. Barring Mexicans from coming across the border is not going to magically reopen shuttered car and tractor factories. On the contrary, if you could even plausibly tamp down the inflow, you would only increase the out-migration of American business. When a 2,000-mile border separates two nations with as much as a 20-to-1 wage gap, what do you think is going to happen?

Our national economy easily absorbs and desperately needs about a million and a half immigrant workers per year to grow and compete. We let a million of them come in legally. The other half-million we make run and dart across the border at great peril. Our reality has outstripped our laws — and our way of framing the issue. In the end, it will make little difference who prevails in this year’s congressional debate, as nothing will change on the ground — backlash or not. It’s a lot like debating the tides.

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