1st Amendment.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
Stop the Presses: Lincoln Suppresses Journalism
Pending more information and suffering from insomnia. Looks like the Lincoln Administration in the Crisis of war took a strict view of that military necessary trumped freedom of the press. Pending SCOTUS ordering a President to Stop, there is no overt prohibition of shutting down the press in wartime in 1860.
In the wake of this tightened oversight, some Democratic war opponents tried arguing that constitutional guarantees of free speech and free press must remain absolute no matter what the danger of an armed revolt. Even Lincoln’s friend Edward Baker, in one of his final speeches in the U.S. Senate before accepting his fateful military commission, insisted that neither the eradication of slavery nor the preservation of the Union justified threats to “the liberty of the press.” Critics pointed out that the First Amendment unequivocally guaranteed: “Congress shall make no law…abridging the freedom of speech, or of the press.” And Congress never did. This did not inhibit the administration from determining that in an unprecedented case of rebellion, and under the powers the president had claimed in order to crush it, military necessity superseded constitutional protection, and contingency trumped the organic assurances of freedom of expression within the Bill of Rights.
We have different suppressions. Some were for military secrets, some suppressed pro-secession sentiment from being published.
Based on this argument, the administration began conducting—or, when it occurred spontaneously, tolerating—repressive actions against opposition newspapers. At their most unobjectionable level, the safeguards were initially meant to keep secret military information off the telegraph wires and out of the press. But in other early cases censors also prevented the publication of prosecession sentiments that might encourage border states out of the Union. In an anonymous dispatch for the New York Examiner, presidential clerk William Stoddard probably spoke for the White House in complaining that, cut off from their usual sources, “the legion of daily newspaper reporters” roamed “the streets and camps…pouncing, with hawk-like avidity, upon every poor little stray item which, in their palmier days, they would have scorned to notice.” And some of those “items,” the administration believed, should remain secret.
No written trail of Lincoln's suppression of the press exists, however, Lincoln did not muzzle those who did.
Eventually the military and the government began punishing editorial opposition to the war itself. Authorities banned pro-peace newspapers from the U.S. mails, shut down newspaper offices and confiscated printing materials. They intimidated, and sometimes imprisoned, re – porters, editors and publishers who sympathized with the South or objected to an armed struggle to restore the Union. For the first year of the war, Lincoln left no trail of documents attesting to any personal conviction that dissenting newspapers ought to be muzzled. But neither did he say anything to control or contradict such efforts when they were undertaken, however haphazardly, by his Cabinet officers or military commanders. Lincoln did not initiate press suppression, and remained ambivalent about its execution, but seldom intervened to prevent it.
No numbers yet, the 300 number show up in lots of spots, but no references.