William A. Crafts, Life of Ulysses S. Grant: His Boyhood, Campaigns, and Services, Military and Civil.

[24] knowing that it was war, and no game of politics, in which the country was engaged. He established his headquarters at Cairo, at the mouth of the Ohio, on the 4th of September, and at once set himself at work not only to strengthen that important point, but to secure the safety of his district, and commence operations against the enemy. On the day of his arrival at Cairo, the rebels were the first to violate the assumed neutrality of Kentucky by occupying Columbus, a strong position on the Mississippi. Grant saw the danger of this movement, and determined to check any further advance by at once entering Kentucky with the Union forces. He prepared to take possession of Paducah, at the confluence of the Tennessee River and the Ohio. Having notified General Fremont of his intention, and receiving no objection from that officer, he started for Paducah on the night of the 5th. He also notified the governor of Kentucky, and was rebuked by Fremont for holding any communication with state authorities, except through his superior officer. But Grant made no complaint of this, or any other disapproval of his course; for though he felt fully justified by his own calm judgment, he was a thorough soldier, and was always subordinate. He occupied Paducah, and secured it against a rebel force which was approaching, and against the treachery of malignant rebel residents. By the real Union men his movement was hailed with joy; and notwithstanding the complaints of those who loudly asserted the neutrality of Kentucky, that state was, by that prompt movement, secured to the Union cause. After the deed was done, Grant received permission from Fremont to attempt it “if he felt strong enough.”