“What about Reagan in 1987? And George H.W. Bush in 1990?”

This has become a favorite Democratic and center-left rebuttal to Republicans angry at reports that President Obama may soon grant residency and working papers to as many as 5 million illegal aliens. If Obama acts, he’d rely on precedents set by Republican predecessors. Surely that should disbar today’s Republicans from complaining?

Surely not, and for four reasons.

1) Reagan and Bush acted in conjunction with Congress and in furtherance of a congressional purpose. In 1986, Congress passed a full-blown amnesty, the Simpson-Mazzoli Act, conferring residency rights on some 3 million people. Simpson-Mazzoli was sold as a “once and for all” solution to the illegal immigration problem: amnesty now, to be followed by strict enforcement in future. Precisely because of their ambition, the statute’s authors were confounded when their broad law generated some unanticipated hard cases. The hardest were those in which some members of a single family qualified for amnesty, while others did not. Nobody wanted to deport the still-illegal husband of a newly legalized wife. Reagan’s (relatively small) and Bush’s (rather larger) executive actions tidied up these anomalies. Although Simpson-Mazzoli itself had been controversial, neither of these follow-ups was.

Executive action by President Obama, however, would follow not an act of Congress but a prior executive action of his own: his suspension of enforcement against so-called Dreamers in June 2012.

A new order would not further a congressional purpose. It is intended to overpower and overmaster a recalcitrant Congress. Two presidents of two different parties have repeatedly called upon Congress to pass a second large amnesty. Congress has repeatedly declined. Each Congress elected since 2006 has been less favorable to amnesty than the previous one, and the Congress elected this month is the least favorable of all. Obama talks as if Congress’s refusal to fall in with his wishes somehow justifies him in acting alone. He may well have the legal power to do so. But it hardly enhances the legitimacy of his action. Certainly he is not entitled to cite as precedent the examples of presidents who did act together with Congress.

2) Reagan and Bush legalized much smaller numbers of people than Obama is said to have in mind. While today's advocates cite a figure of 1.5 million people among those potentially affected by Bush's order, only about 140,000 people ultimately gained legal status this way, according to U.S. Immigration and Customs Enforcement data as reviewed by Mark Krikorian of the Center for Immigration Studies. (Updated: Krikorian reconsidered the numbers and now concludes the true figure is even lower—less than 50,000.) Obama’s June 2012 grant of residency to the so-called “Dreamers”, people who were brought to the United States illegally as children, could potentially reach 1.4 million people. His next round of amnesty, which is advertised as benefiting the parents of the Dreamers and other illegal-alien parents of U.S. resident children, could reach as many as 5 million people.

Put it another way: If all the potential of Obama’s past and next action is realized, he would—acting on his own authority and in direct contravention of the wishes of Congress—have granted residency and work rights to more than double the number of people amnestied by Simpson-Mazzoli, until now the most far-reaching immigration amnesty in U.S. history.

As the philosopher liked to point out, at a certain point, a difference in quantity becomes a difference in quality.

3) The Reagan-Bush examples are not positive ones. The 1986 amnesty did not work as promised. It was riddled with fraud. The enforcement provisions were ignored or circumvented. Illegal immigration actually increased in the years after the amnesty. The supposed "once and for all” solution almost immediately gave rise to an even larger version of the original problem.

The argument that “Reagan and Bush did it,” is essentially an argument that future generations should not learn from the errors of previous generations. With the advantage of experience, it is clear that their decisions did not produce the desired result, and actually greatly worsened the problem they sought to solve. Let’s not repeat their mistake.

4) The invocation of the Reagan and Bush cases exemplifies the bad tendency of political discussion to degenerate into an exchange of scripted talking points. “Oh yeah? Well, this guy you liked also did this thing you don’t like!” Is that really supposed to convince anybody? What we have here is not a validation of the correctness of President Obama’s action. It’s the shaking of a fetish, an effort to curtail argument rather than enlighten it.

It’s a style of argument borrowed from the late-night cable-comedy shows, in which a clip of somebody saying something at some point in the past is supposed to estop that person—or anybody in any way connected to him, or supportive of him, or even mostly but not entirely admiring of him—from ever saying anything different in the future. But a zinger is not a rebuttal. In this case, with all the huge differences between Obama’s situation and those of his predecessors, it does not even zing.