WASHINGTON — It is sometimes argued, rather piously, that the outcome of the immigration reform debate must be decided on the substance instead of the politics. And there is much to commend in the substance of the Senate bill, which would improve security at the border, modernize employer verification, shift future green cards toward more skilled applicants and provide undocumented workers a chance to demonstrate they are good citizens (paying fines and back taxes and avoiding a criminal record), before they are sworn in as citizens 13 years down the road.

But if there is any issue where politics is unavoidable, it is this one: Immigration policy (along with demographic trends) determines the shape of the future electorate. It is not particularly realistic, or even coherent, to argue that defining the boundaries of the political community should not be sullied by politics.

So the current, internal Republican debate on the political implications of reform is unavoidable. Some believe the shift toward a more welcoming immigration policy is a precondition for appealing to rising ethnic groups. Others claim that undocumented workers, in the words of one Republican congressman, Michael Burgess of Texas, are "11 million undocumented Democrats" who would, as citizens, vote the GOP into irrelevance.

The Republican camps in this dispute are largely defined by their answer to a prior political question: Does the current coalition of the GOP need to be motivated or modified? If it is possible to win future national elections by increasing the enthusiasm and turnout of current Republican voters, then embracing immigration reform is an unnecessary political risk. If the Republican coalition is unsustainable and requires transformation, then the assumption of political risk is required.

For two reasons, Republicans should be leaning toward the modification of their coalition.

First, the realities of demographic change have begun to bite. Since the mid-1990s, the share of nonwhite voters has steadily increased by about three percentage points each presidential election. If America's demographic composition were the same last year as it was in 1992, Mitt Romney would have won in a landslide. If it were the same as it was in 2000, he would now be president. Instead, Romney secured 59 percent of the white vote — and lost the election by four points.

Second, during the same 20 years these shifts were taking place, elements of the GOP undertook an active campaign to alienate rising demographic groups. It began with Proposition 187 in California, denying public services to illegal immigrants and their families, and continued with restrictive immigration laws in Arizona, Georgia, South Carolina and Alabama. This effort symbolically culminated in Romney's embrace of "self-deportation" and his loss of the Hispanic vote by 44 points.

From one perspective, immigration restrictionists are correct. In the current political atmosphere — the atmosphere they helped to create — immigrants who become citizens will be deeply suspicious of Republicans. So are current voters who have ties to or sympathy for immigrant communities. The problem is this: While killing immigration reform may slightly extend the viability of the current Republican political coalition, it may seriously undermine the attempt to adjust it.

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Such an adjustment depends on Hispanic voters being gettable by Republicans — which many restrictionists deny. Hispanics, it is argued, are inherently favorable to big government. But there is some paradoxical hope to be found for the GOP in the recent collapse of its appeal among Hispanics. This did not happen because immigrant groups became more liberal or more welfare-dependent. It happened because Republicans seemed more hostile to their interests. Clearly there is some elasticity in Latino political opinion. A GOP political strategy might begin by removing the stick they have put in the eye of a rising demographic group — the main political argument for supporting immigration reform.

This won't be enough. While appealing to Hispanic voters is not like appealing to Manhattanites — it doesn't involve the abandonment of social conservatism — it does require a populist economic agenda. Recent immigrants are naturally concerned about a working social safety net, a working public education system, and a working job training system. Republicans will need to offer serious reform proposals in these areas. And this requires a positive, active, market-oriented role for government that competes with more centralized and bureaucratic Democratic approaches.

The GOP's political goal is modest. It doesn't need to win majorities among minorities, just avoid lopsided losses. But the challenge is larger than it first appears — not merely to accept an immigration bill, but to start a period of ideological creativity and persistent outreach.

Michael Gerson's email address is michaelgerson@washpost.com.