He was defeated of a re-election to the Senate by Henry S. Geyer, a pro-slavery Whig, and supporter of the Jackson resolutions, after having filled a seat in that august body for a longer time consecutively than any other senator ever did. Thus was removed from the halls of Congress the most sagacious and formidable enemy that the disunion propagandists ever encountered. Their career in Congress and in the control of the federal government was thenceforth unchecked. The cords of loyalty in Missouri were snapped in Benton's fall, and that State swung off into the strongly-sweeping current of secessionism. The city of St. Louis remained firm a while, and returned Benton twice to the House; but his energies were exhausted now in defensive war; and the truculent and triumphant slave power dominating, the State at last succeeded, through the coercion of commercial interests, in defeating him even in the citadel of loyalty. He tried once more to breast the tide that had borne down his fortunes. He became a candidate for governor in 1856; but, though he disclaimed anti-slavery sentiments, and supported James Buchanan for President against Fremont, his son-in-law, he was defeated by Trusten Polk, who soon passed from the gubernatorial chair to Benton's seat in the United States Senate, from which he was, in course of time, to be expelled. Benton retired to private life, only to labor more assiduously in compiling historical evidences against the fast ripening treason of the times. The Missouri senator was no longer in the way of the Southern oligarchs. A shaft feathered by his own hands--the doctrine of instructions--had slain him.