The Constitution called for fresh interpretation in the light of the Civil War and its results.
The first theory of reconstruction may be found in the Crittenden-Johnson resolutions of July 1861, which declared that the war was being waged to maintain the Union under the Constitution and that it should cease when these objects were obtained.

This would have been subscribed to in 1861 by the Union Democrats and by most of the Republicans, and in 1865 the conquered Southerners would have been glad to reenter the Union upon this basis; but though in 1865 the resolution still expressed the views of many Democrats, the majority of Northern people had moved away from this position.
The attitude of Lincoln, which in 1865 met the views of a majority of the Northern people though not of the political leaders, was that "no State can upon its mere motion get out of the Union," that the States survived though there might be some doubt about state governments, and that "loyal" state organizations might be established by a population consisting largely of ex-Confederates who had been pardoned by the President and made "loyal" for the future by an oath of allegiance.
Reconstruction was, Lincoln thought, a matter for the executive to handle.

But that he was not inflexibly committed to any one plan is indicated by his proclamation after the pocket veto of the Wade-Davis Bill and by his last speech, in which he declared that the question of whether the seceded States were in the Union or out of it was "merely a pernicious abstraction." In addition, Lincoln said: "We are all agreed that the seceded States, so called, are out of their proper practical relation with the Union, and that the sole object of the government, civil and military, in regard to those States is to again get them into that proper practical relation.

I believe that it is not only possible, but in fact easier, to do this without deciding or even considering whether these States have ever been out of the Union, than with it.

Finding themselves safely at home, it would be utterly immaterial whether they had ever been abroad.