It is said he expanded his power with alarm. He was a accused of becoming a tyrant nd warned that his assertions of authority under the guise of "commander in chief" threatened the viability of a constitutional democracy.
When Union troops were assaulted in Baltimore, Lincoln suspended habeas corpus along the Philadelphia to Washington line, that was one of the dramatic actions to that point, then he faced the legal question whether he had the authority to do that. He believed that with the country in a state of rebellion, he had "war powers", a concept that was not in the Constitution. Some politics accused him of "executive usurpation" and censured him of "unconstitutional acts".
He always used to say that the powers he claimed were war measures, and as soon as the war was over, he would relinquish them.