Protesters from United We Dream stage a sit-in at the state office of Senate Majority Leader Harry Reid, D-Nev., on Capitol Hill in Washington, Tuesday, Sept. 9, 2014. Dreamers, undocumented immigrants who came to the United States as children, are upset with President Barack Obama's decision to not act on immigration reform until after Novermber's midterm elections. (J. Scott Applewhite/AP)

PRESIDENT OBAMA’S zigs and zags in pursuit of immigration reform are a long-unfolding narrative now assuming epic dimensions. In the latest installment, Mr. Obama has postponed the unilateral reforms he promised to have unveiled by now. He did so not for any high-minded purpose but rather to avoid dealing mortal blows to the reelection of a handful of Democratic senators who begged the president to hold off.

Thus has subverting immigration reform become a bipartisan project advanced by Republicans, who despise the idea of putting millions of Hispanics on a path to citizenship, and by Democrats, who like it but fear the political fallout.

Mr. Obama insists that congressional inaction justifies his determination to take matters into his own hands and refashion enforcement of the nation’s laws to his liking. In his view, executive action is warranted by legislative paralysis; he alone will determine (though not quite yet) the breadth and depth of changes that could affect the status of millions of undocumented immigrants.

The president’s goals are right; his method, depending on how far he goes, seems ill-advised. Until he outlines his legal justification, if he eventually proceeds unilaterally as promised, no firm judgment can be offered. But his options seem limited if he intends to carry out the sort of sweeping changes that advocates of reform are counting on.

Just a year ago, Mr. Obama told an interviewer that it “would be very difficult to defend legally” any move to shield large numbers of additional illegal immigrants from deportation as he did in 2012 for so-called Dreamers — undocumented migrants brought to this country as children.

Other ways for the president to protect immigrants from deportation, including granting administrative “parole,” have never been used — and are not intended — for huge categories of millions of individuals facing possible deportation.

Whether Mr. Obama may be able to make stick such a blanket change in enforcement is one question; he probably can. A separate question is whether it’s wise.

His decision to postpone an action he promised for the end of the summer, for fear of the electoral fallout, underscores the enormity of the likely political backlash. By ignoring Congress and sidestepping normal procedures — the same procedures he himself followed for several years in hopes for immigration reform — Mr. Obama does the nation no favors.

We share the president’s conviction that the immigration system is a mess; that Congress — specifically, House Republicans — has abdicated its responsibility and defied popular will by refusing to fix it; and that the status quo of 11 million undocumented immigrants is economically self-defeating.

But rewriting the law unilaterally in defiance of Congress and on dubious legal grounds, even after the midterm elections, will not ultimately serve the cause of durable reform. It is more likely to ignite a political firestorm that will give the upper hand to immigration restrictionists, who would use it for years to justify resistance to reform. For the president, that would be a pyrrhic victory indeed.