Senate Republican leader Mitch McConnell of Kentucky. (J. Scott Applewhite/AP)

THE DAY after Republicans trounced Democrats in the midterm elections, leaders of both parties sent encouraging signals that they might work together better than they did during the last two dismal years. Presumptive Senate Majority Leader Mitch McConnell (R-Ky.) promised to get that chamber working again and to search for areas of agreement between a Republican Congress and President Obama; he mentioned trade agreements and tax reform as priorities. Shortly afterward, Mr. Obama vowed to consider Republican ideas with an open mind and to reach out to Mr. McConnell and House Speaker John Boehner (R-Ohio), both of whom he will host at the White House on Friday. The president, too, said he sees potential for agreement on trade and taxes, as well as on improving American infrastructure.

Yet deep fissures were also visible, and one — the split over immigration — threatened to sabotage the new beginning Mr. Obama and his GOP counterparts claimed to want. Mr. McConnell warned that unilateral presidential action giving temporary legal status to undocumented workers would amount to “waving a red flag in front of a bull,” poisoning the well instead of building trust between lawmakers and the White House. Though Mr. Obama later claimed that it is his “profound preference and interest to see Congress act,” he nevertheless promised to take unilateral action on immigration before the end of the year, insisting that he can’t “just wait.”

In fact, he should do just that — wait.

We sympathize with the president. He is certainly right on the policy: It’s important to bring hardworking undocumented immigrants out of the shadows. Sizable majorities of Americans agree. For years, he has held back from using his executive authorities to rationalize the system. In the meantime, he has tried to better enforce existing policies, including by deporting more people. He also encouraged the Senate to pass a comprehensive bill, which it did. He then gave Mr. Boehner space to get the legislation passed in the House, which the speaker could not manage. Anyone might be fed up.

Yet on Wednesday Mr. Obama himself argued that the recent election has the potential to loosen the gridlock in Washington. A united GOP Congress with large Republican majorities might manage to do more than previous Congresses in which Republicans were powerful but less invested. If he believes that, the president should give Mr. McConnell the opportunity to make good on some of the lofty promises he has made since the Republican victory. Mr. Obama could seize the moral high ground and test GOP leaders’ seriousness about cooperating by offering them time to show they can act, including on immigration. The cost would not be very high; holding back a provocative executive action does not preclude the president from issuing one in six months’ or a year’s time, should Republican leaders fail to make good on their conciliatory tone.

In the meantime, the president can pursue deals on trade, taxes, infrastructure and other policies on which there is authentic potential for agreement. The right response to the Republicans’ election victory is not a poke in the eye.