That was not Lincoln's obligation. His obligation was to see that the laws were faithfully executed and that the Constitutional Union was protected. In a wartime situation, the suspension of the writ was both correct and necessary.
If Congress, who you claim had sole authority to suspend the privilege of the writ (regardless of the situation), had objected to Lincoln's action, they could have made it known. Instead, they approved of his actions.
If he was purporting to suspend it, it was!
His obligation was to see that the laws were faithfully executed and that the Constitutional Union was protected.
Fine! Then he failed at that test as well by failing to faithfully execute the Judicial Act of 1789.
If Congress, who you claim had sole authority to suspend the privilege of the writ (regardless of the situation), had objected to Lincoln's action, they could have made it known.
They did by killing his bill in 1861.
It is never correct and proper for a MILITARY officer to suspend the privilege of the writ of habeas corpus on his own authority and at his own discretion.
In Merryman, there was no suspension by anybody. General Keim ordered the arrest, but he was in Pennsylvania and could not assume lawful authority to suspend the writ in Maryland, not even according to the authorization given by Lincoln to General Scott.
General Cadwalader did not know a thing about it until after the fact. The letter purporting to give suspension authority to General Cadwalader was sent after the proceedings in court had already concluded.
Most assuredly, Lincoln did not suspend the privilege of the writ himself in the Merryman case.