You have to truncate the sentence. You are pushing something not at all supported in the record.
"I felt that measures, otherwise unconstitutional, might become lawful, by becoming indispensible to to the preservation of the of the Constitution, through the preservation of the nation. Right or wrong, I assumed this ground, and now avow it."
Lincoln is clearly saying that the EP was lawful because it became indispensible. He -thought- it to be lawful. Your earlier statement that "even Lincoln" thought the EP was unlawful is just a lie.
Walt
In your world, does that mean legal or illegal?