If a paper was pro-slavery, did that automatically mean it was biased against the North. Perhaps it was just biased against abolitionists. Besides, it was Nicolay and Hay and not the paper who made the statement that the editors of the Intelligencer had made a careful study and had no reason to be biased. If the paper's findings were really biased and not correct in their opinion, one would expect Nicolay and Hay to say so.
But William Lloyd Garrison had little love for the paper [the National Intelligencer: it had published a letter offering a reward to any one who delivered him "dead or alive into the hands of the authorities of any state south of the Potomac."
Wasn't it Garrison who said, "The Union is a lie. The American Union is an imposture, and a covenant with death, and an agreement with hell. ... I am for its overthrow. ... Up with the flag of disunion ..." ?
It's probably just as well Lincoln didn't hear him say it. Garrison might have been tossed in jail like others for months without charges for speaking favorably of disunion. On the other hand, if Union General "Beast" Butler had heard Garrison say "up with the flag of disunion," perhaps he would have hung Garrison a la Mumford.
It is not clear from the two pages I have of the National Intelligencer, what its politics were, but I have no reason to doubt a pro-slavery bias. My pages do mention that members of the Tenth Ohio attacked Negroes in a theater in Nashville in September 1862. I suppose these Union soldiers were biased against the North.
That was what I said. Some could consider such a paper to be "evenhanded" between North and South, even if it was pronouncedly pro-slavery.
But my larger point was that even a paper in a city that still allowed slavery found many personal liberty laws unobjectionable on constitutional grounds, so the problem wasn't as great as it might have appeared at first.