Excellent, Dave! My next clue was going to be the answer is on the Internet.
The quote in context:
"I am curious to know what offense will be set up by the Government in Surratt's case. I am very much afraid the trial will meet with another postponement so that they can urge a longer continuance of my exile on this account. Our country seems a complete mobocracy instead of a Government of law and order.
The President does not feel warranted in the execution of his plainest duties under the Constitution without first consulting the mob spirit."