Oscar Rodriguez, an undocumented immigrant, at a viewing party for a speech by President Obama last year. PHOTOGRAPH BY MARIO TAMA/GETTY

With President Obama set to announce his new immigration policy in a prime-time address on Thursday, which will be followed up with a public event in Las Vegas on Friday, his critics, and some of his erstwhile supporters, are busy giving him a lecture on civics and the Constitution. All indications are that the President will lift the threat of deportation from several million undocumented foreigners, perhaps more, enabling them to stay here and work.

In some circles, it’s not so much the policy itself that is causing outrage. It’s the sight of the President invoking his executive powers to do an end run around a Congress that has failed to agree on immigration reform. Some of Obama’s critics are throwing at him a selection of his previous statements, in which he said that he couldn’t single-handedly rewrite immigration laws. “In Mr. Obama’s own words, acting alone is ‘not how our democracy functions,’ ” the Washington Post opined in an editorial. In the Times, David Brooks said Obama’s move, if it goes ahead, “would further destabilize the legitimacy of government.”

These are some heavy charges to hurl at a former lecturer in constitutional law, especially since many experts on the immigration statutes agree that he has the legal authority to do what he is apparently planning. From Ronald Reagan to George H. W. Bush to Bill Clinton to George W. Bush, all recent Presidents have, at some point, unilaterally granted immunity from deportation to various groups, citing the federal government’s “prosecutorial discretion” over whether to enforce the immigration laws that are on the books. Back in September, a hundred professors of immigration law wrote an open letter to Obama, which cited some of the historical precedents and some of the relevant case law. The latter included a ruling from the Supreme Court that came as recently as 2012, which said, “A principal feature of the removal system is the broad discretion exercised by immigration officials. ... Federal officials, as an initial matter, must decide whether it makes sense to pursue removal at all.”

There can be little doubt that Obama’s actions will affect many more people than previous Presidential edicts, which include Reagan’s 1987 decision to allow about two hundred thousand exiles from Nicaragua to stay in the United States, and Clinton’s 1998 move to limit deportations of Haitians. According to news accounts, up to five million undocumented immigrants could be affected this time.

However, many authorities on immigration law believe that the potential scale of the program doesn’t necessarily impact the President’s freedom to maneuver. During a recent panel session in Washington, which the Huffington Post ’s Sam Stein wrote about, Christopher Schroeder, a professor at Duke Law School, said, “I don’t know where in the Constitution there is a rule that if the President’s enactment affects too many people, he’s violating the Constitution. ... I agree this can make us very uncomfortable. I just don’t see the argument for unconstitutionality at this juncture.”

Perhaps the strongest argument put forward by Obama’s critics is the one that says he is establishing a dangerous precedent. If Obama can do this, the argument goes, what’s to stop a future Republican President from, say, telling the Internal Revenue Service not to collect the fines attached to the individual mandate to buy health insurance? Even though the individual mandate may not be the best example to use—I took it from the Washington Post editorial—the question is nevertheless fair. During the Bush Administration, some Democrats protested loudly, and with good reason, at President Bush’s efforts to expand his executive authority in the areas of national security and domestic surveillance.

The best defense of Obama’s decision, I think, is a historical one, and it goes to the cognitive dissonance that has long been associated with immigration policy in this country. For many, many years, the United States operated two different immigration systems. One of them, which existed largely on paper, was a pretty harsh thing, with firm numerical quotas, effective border security, and harsh punishments for undocumented aliens who violated the laws. The other immigration system, which existed in practice, was effectively a policy of Don’t Ask, Don’t Tell. Once undocumented foreigners made it across the border, they were largely left alone. Even as they were forced to subsist in the gray economy, with few rights and little access to public services, they could work, save, and, in many cases, buy homes and have families. As long as they didn’t get into serious trouble with the law, nobody bothered them much.

This dual system was allowed to survive because most Americans liked it. They didn’t care for the idea of the border going unprotected, or of the country being overwhelmed by impoverished Latin Americans. Hence, there had to be some laws on the books to prevent this from happening. But Americans liked the cheap labor and cheap services that undocumented immigrants provide. They liked the economic vibrancy that immigrants bring with them. And they liked the idea of living in a country that was built on immigration and celebrated diversity.

Despite occasional outbursts of nativism and anti-foreigner sentiment, particularly in the border states, there was little of the widespread xenophobia that exists in many other countries. Indeed, there was a bipartisan recognition, sometimes implicit, that most undocumented immigrants worked hard, served an important economic function, and, ultimately, deserved some sort of recognition. In 1986, Congress passed new immigration laws that granted legal status to immigrants who could show that they had been in the country since before 1982. In 1990, George H. W. Bush, acting on his own authority, extended the 1986 law to include family members of immigrants covered by the previous legislation.

Since then, a lot has changed. But despite the rise of the Minutemen, the Tea Party, and various other right-wing rabble-rousers, anti-immigrant sentiment is still confined to the minority. That’s one of the reassuring things about America. A new NBC News/Wall Street Journal poll found that fifty-seven per cent of Americans support the establishment of a pathway to legal status for the undocumented. And, despite all the talk of a backlash among white people against Obama’s policies, more than fifty per cent of whites support such a pathway, as well.

What is different now is that an influential segment of the Republican Party, shouted on by a motley assortment of nativists, conservative activists, and media enragés, has decided to upend the informal immigration system, the permissive one, and replace it with a fully functioning version of the far more draconian system that previously only existed on the statute books—with high walls, rigid enforcement, and mass deportations. Reneging on the implicit deal that underpinned the Don’t Ask, Don’t Tell policy, these Republican ultras have also turned against immigrants who have already been here for years, refusing to countenance any sort of amnesty, even one confined to law-abiding people who, through no choice of their own, were brought to this country as children—the so-called Dreamers. In 2012, when Obama issued an executive order to prevent deportations from this group, conservative Republicans vigorously opposed it and vowed to overturn it.

In immigration policy, as in other areas, it was the rightward shift in the G.O.P. that drove Obama, after almost six fruitless years of seeking a legislative agreement, to overcome his obvious reluctance to invoke, in such a large way, his executive authority. By doing it now, just a few weeks after his party suffered a heavy defeat in the midterms, he is taking a big risk. Although Americans generally support extending to undocumented immigrants some prospect of achieving legal status, they aren’t very keen on Presidents going it alone. In that NBC News/Wall Street Journal poll, just thirty-eight per cent of respondents said they favored Obama taking executive action without receiving approval from Congress.

How the new executive order will play out politically, nobody can say for sure. Several House Republicans have already said that they will go to court to try to block it. Even if this bid fails, which seems likely, the President’s gambit will surely color the new Congress when it gathers in the new year. And, with the 2016 primary season little more than a year away, the various candidates will be eager to stake out positions on the issue. (On the G.O.P. side, some of the possible contenders have already begun to do so.)

The partisan battle is about to begin—or, rather, begin again. Nothing can prevent that from happening. But what can and should be challenged is the notion that Obama is the radical here. In terms of how the United States treats immigrants, as opposed to what is on the statute books, he’s the one defending the traditional way of doing things.