Clause qualifies the scope of political discretion heretofore recognized as belonging to Congress in regulating the entry and deportation of aliens. And since the intrinsic consequences of deportation are so close to punishment for crime, it might fairly be said also that the ex post facto Clause, even though applicable only to punitive legislation, [Footnote 4] should be applied to deportation.
But the slate is not clean. As to the extent of the power of Congress under review, there is not merely "a page of history," New York Trust Co. v. Eisner, 256 U. S. 345, 256 U. S. 349, but a whole volume. Policies pertaining to the entry of aliens and their right to remain here are peculiarly concerned with the political conduct of government. In the enforcement of these policies, the Executive Branch of the Government must respect the procedural safeguards of due process. The Japanese Immigrant Case, 189 U. S. 86, 189 U. S. 101; Wong Yang Sung v. McGrath, 339 U. S. 33, 339 U. S. 49. But that the formulation of these policies is entrusted exclusively to Congress has become about as firmly imbedded in the legislative and judicial tissues of our body politic as any aspect of our government.