Distilled to their discouraging essence, Republicans’ reasons for retreating from immigration reform reflect waning confidence in American culture and in the political mission only Republicans can perform — restoring America’s economic vigor. Without this, the nation will have a dismal future only Democrats can relish: government growing in order to allocate scarce opportunity.

Many say addressing immigration will distract from a focus on ObamaCare. But a mature party avoids monomania, and ObamaCare’s defects are obvious enough that voters won’t require nine more months of reminders.

Many Republicans say immigration policy divides their party. If, however, the party becomes a gaggle of veto groups enforcing unanimities, it will become what completely harmonious parties are: small.

Many Republicans see in immigrants only future Democratic votes. Yet US history tells a consistent story — the party identified with prosperity, and hence opportunity, prospers.

Many Republicans have understandable cultural concerns, worrying that immigrants from this hemisphere do not experience the “psychological guillotine” that severed trans-Atlantic immigrants from prior allegiances. But is there data proving that American culture has lost its assimilative power? Thirty-five percent of illegal adult immigrants have been here at least 15 years, 28 percent for 10 to 14 years and only 15 percent for less than five years. Thirty-five percent own their homes. Are we sure they are resisting assimilation?

Many Republicans rightly say control of borders is an essential ingredient of national sovereignty. But net immigration from Mexico has recently been approximately zero. Border Patrol spending quadrupled in the 1990s and tripled in the 2000s. With illegal entries near a 40-year low, and a 2012 Government Accountability Office assessment that border security was then 84 percent effective, will a “border surge” of $30 billion more for the further militarization (actually, the East Germanization) of the 1,969 miles assuage remaining worries?

Many say President Obama can’t be trusted to enforce reforms. This is no reason for not improving immigration laws that subsequent presidents will respect. Besides, the Obama administration’s deportations are, if anything, excessive, made possible by post-9/11 technological and manpower resources. As The Economist tartly notes, “A mass murder committed by mostly Saudi terrorists resulted in an almost limitless amount of money being made available for the deportation of Mexican house-painters.”

Many say immigration runs counter to US social policies aiming to reduce the number of people with low levels of skill and education, and must further depress the wages of Americans who, at the bottom of the economic ladder, are already paying the price for today’s economic anemia. This is true. But so is this: The Congressional Budget Office says an initial slight reduction of low wages (0.1 percent in a decade) will be followed by increased economic growth partly attributable to immigrants.

Immigration is the entrepreneurial act of taking the risk of uprooting oneself and plunging into uncertainty. Small wonder, then, that immigrants are about 20 percent of owners of small businesses, and that more than 40 percent of Fortune 500 companies were founded by immigrants or their children.

George W. Bush was the first president since Woodrow Wilson to serve two terms and leave office with the average household income lower than when he entered it. Obama may be the second when he leaves during the eighth year of a wretched recovery.

Forty-seven percent of the House Republican conference has been in Washington 37 months or less; 21 percent never held any other elective office. Many plunged into politics because they were dismayed about the nation’s trajectory under the current president and his predecessor. Many have only dim memories of a more dynamic America, and have little aptitude for politics suited to, and aimed at restoring, vibrancy.

Progressives often are ambivalent about scarcities because they see themselves as administrators of rationing. But President Bill Clinton, refuting opposition (much of it from Democrats) to the North American Free Trade Agreement, splendidly said: “Protectionism is just a fancy word for giving up.”

Opposition to immigration because the economy supposedly cannot generate sufficient jobs is similar defeatism. Zero-sum reasoning about a fixed quantity of American opportunity is for an America in a defensive crouch, which is not for conservatives.

georgewill@washpost.com