Lincoln didn't violate the Constitution.
"Lincoln, with his usual incisiveness, put his finger on the debate that inevitably surrounds issues of civil liberties in wartime. If the country itself is in mortal danger, must we enforce every provision safeguarding individual liberties even though to do so will endanger the very government which is created by the Constitution? The question of whether only Congress may suspend it has never been authoritatively answered to this day, but the Lincoln administration proceeded to arrest and detain persons suspected of disloyal activities, including the mayor of Baltimore and the chief of police."
--Chief Justice William Rehenquist, November, 1999
"The President was not out to trample on the First Amendment. He was not out to crush his political opposition. He suspended the writ of Habeas Corpus in response to perceived military threats to the Union. After he, and later Congress, removed that Constitutional safeguard, the Lincoln Administration did not use its power selfishly or arbitrarily. It arrested only those people who actively supported the Confederate war machine--people like Merryman, who recruited troops to march south. And when people walked this fine line between political dissent and treason, as Vallandigham did, Lincoln tried to err on the side of free speech...
Midway through the war, Lincoln predicted that Habeas Corpus would quickly be re-instituted after the war was over. He could not bring himself to believe that Americans would allow the wartime suspension of Habeas Corpus to extend into peacetime, he said, "Any more than I am able to believe that a man could contract so strong an appetite for emetics during temporary illness as to persist in feeding upon them during the remainder of his healthful life." Lincoln died before he could see the writ of habeas corpus restored.
Lincoln asked:
"What constitutes the bulwark of our own liberty and independence? It is not our frowning battlements, our bristling sea coasts, the guns of our war steamers, or the strength of our gallant and disciplined army. These are not our reliance against a resumption of tyranny in our fair land. All of them may be turned against our liberties, without making us stronger or weaker for the struggle. Our reliance is in the love of liberty which God has planted in our bosoms. Our defense is in the preservation of the spirit which prizes liberty as the heritage of all men, in all lands, everywhere. Destroy this spirit, and you have planted the seeds of despotism around our doors. Familiarize yourselves with the chains of bondage, and you are preparing your own limbs to wear them. Accustomed to trample on the rights of those around you, you have lost the genius of your own independence, and become the fit subjects of the first cunning tyrant who rises."
So today, let us heed the wisdom of a man who led our nation to a "new birth of freedom." Let us always be, first and foremost, lovers of liberty."
-- Justice Sandra Day O'Connor, 11/19/96
Lovers of liberty -- like President Lincoln
Walt
It has never been ruled that Lincoln violated the Constitution at all. But you should really direct that question to Jeff Davis. There was a reason, I think, why the confederate president was not required to swear an oath to protect and defend the confederate constitution. They had so little respect for it to begin with.