It's called the Constitution.
Oh, the Constitution! But the Constitution doesn't say, "Officers of the government must leave Lambdin P. Milligan strictly alone," does it?
No, it says that the Writ of HC must not be suspended except when yadda yadda yadda...and it doesn't specify who may suspend the Writ, and it says not a word about the president.
There was no -law- that said the president must not suspend the Writ (remember that Milligan sued out on a Writ of HC AFTER LINCOLN WAS DEAD), and there was no case law to guide the executive.
You just look silly.
Walt