When Donald J. Trump takes office on Jan. 20, he will have immense but not unlimited power at his disposal. Back in June, I wrote that he could — even without congressional consent — execute much of his vision. He could, for example, shift enforcement priorities against unauthorized immigrants, probably bar Muslims from entering the country, raise tariffs, withdraw forces from the Middle East, and tear up trade treaties and military alliances.

But there were limits: He could not build a border wall without a congressional appropriation, impose the death penalty on killers of police officers, or strengthen libel laws so that he could sue newspapers that criticized him.

That was then. Because Mr. Trump enjoys Republican majorities in both houses of Congress, his power is even greater. If he can get Republican members of Congress to go along with him, he can do pretty much anything not banned by the Constitution. He can repeal Obamacare, cut taxes and build his border wall. But limits remain.

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