ROSS DOUTHAT has been arguing for the pastweek that Barack Obama's unilateral immigration-policy changes pose a threat of "presidential caesarism". The power grab Mr Douthat is most vexed about involves the so-called DACA ("Deferred Action for Childhood Arrivals") policy, whereby the president has directed authorities to postpone action against undocumented immigrants who arrived as children. Opinions as to whether this oversteps the president’s authority mainly break down along political lines. Defending Mr Obama's actions, Ezra Klein points out that House Republicans have repeatedly blocked immigration-reform legislation, and that when the legislature refuses to act, the executive naturally moves in. Greg Sargent interviews legal experts who note that Mr Obama's policy measures don't actually change the law: rather, authorities lack the resources to prosecute most of the 11.5m illegal immigrants in America, and DACA simply prioritises who should be prosecuted. On the other side, Yuval Levin offers an "outlandish hypothetical": what if a Republican president unilaterally enacted an effective tax cut by ordering the IRS not to prosecute anyone who decided to pay income taxes 10% lower than they had to under law? And Megan McArdle argues that there is a huge difference between simply setting enforcement priorities and "announcing that the law won’t be enforced against a large fraction of the people who are violating it." The most persuasive take, I think, comes from Jonathan Bernstein. He argues that DACA is an illustration of how a Republican Party dominated by its Tea-Party faction gives up control over policy in favour of ideological purity.

[I]n policy area after policy area, House Republicans have said, and demonstrated, that they prefer a worse (for them) substantive result as long as they don’t have to vote for it. Avoiding compromise avoids their greatest fear—being labeled “RINOs”—while allowing them to rail against a “lawless” president. As irresponsible as that might be from the point of view of individual House Republicans, the fact is that their party has set up an incentive structure that pushes them in the “post-policy” direction of choosing symbolic wins at the cost of substantive losses.

This puts the question of a breakdown of the rule of law in a different perspective. There is indeed a difference between a situation in which the vast majority of lawbreakers are not being prosecuted simply because the government lacks the resources to do so, and one in which government has issued explicit public directives that certain kinds of offenders will not (for the time being) be prosecuted. But I think the main threat to the rule of law here comes from a different direction.

A common problem is when the state maintains laws on the books that are out of sync with social reality. Attempting to legislate away the real world—such as the Communist crackdown on market behaviour, or Islamic bans on sexual mores—leads to widespread contempt for the law, and exhausts the resources of government in meting out punishment for standard behaviour. It also empowers officials to act tyrannically: since people are constantly breaking unrealistic laws, authorities can use selective enforcement to extract bribes or punish certain populations disproportionately.

The immigration situation in America falls into this category. The number of undocumented immigrants in the country today dwarfs the resources that authorities possess to arrest and deport them. In fact, most Americans do not want to deport the 11.5m foreigners who are in the country illegally. Polls consistently show large majorities would rather offer them a way to stay, typically by two-to-one margins.

The threat to the rule of law here comes mainly from America's unrealistic immigration policies. The country is a very rich, well-governed country that shares a 3,000-kilometre-long border with a much poorer, badly governed one, which in turn borders countries that are poorer still. Until Central America becomes stable and prosperous, it will continue to send millions of emigrants to the US. Current immigration quotas, which date from 1990, limit each country to no more than 7% of the total of 700,000 legal immigrant visas each year; in principle, Mexico is treated the same as Switzerland. Enforcing this skewed system requires America to constantly raise the already large sums it spends on patrolling the Mexican border; in 2012 America spent $11.7 billion on border security. Fully sealing the border could cost $28 billion per year. The American public (let alone the Republican party) has shown no willingness to appropriate that much money. Deportations rose from 70,000 in 1996 to 419,000 in 2012, with the Obama administration deporting as many people in its first five years as the Bush administration did in eight. Yet this has made no dent in the total population of undocumented immigrants. And the current level of deportation seems to be politically unsustainable. Latino constituents are increasingly fed up.

In essence, there are three kinds of costs to an enforcement-only immigration policy. One is money. Another is the mounting security restrictions of an identity-monitoring police state. (As a Bloomberg View editorial puts it, "With thousands of commercial airports, 7,000 miles of land border and 95,000 miles of shoreline, the US border cannot be sealed without the nation becoming a totalitarian dystopia.") The third is the cruelty which that state must inflict on the people it deports, who are overwhelmingly decent, ambitious, hard-working people striving for a better life for themselves and their children. Are the American people interested in paying that money, complying with that police state, or inflicting that level of cruelty on otherwise upstanding immigrants? Some right-wing Americans may be willing to do so, but most Americans have consistently shown they aren't.

Given all this, America's 11.5m undocumented immigrants aren't going anywhere. The Republican inability to articulate any coherent immigration policy other than "deport them all" amounts to a preference for fantasy over reality, rather than engaging in the messy job of making policy for the real world. America's tolerance of a situation where over 10m of its residents are living here illegally is indeed a threat to the rule of law, and Barack Obama would not be doing the rule of law a service by simply maintaining status-quo policies. The country needs to adjust its immigration policies to fit reality, and if we want that to happen through legislation, the Republicans who control the House need to start governing again.