A politician who deserts his party. The word was used by Earl Malmesbury in this sense in 1792, and this use may have originated with him.

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1800.  Pray sir, what is the meaning of the words, “Rats, Rats, Rats,” in your last Centinel? [It is explained as meaning those who, deserting an apparently sinking ship, resigned their offices.]—The Aurora, Phila., July 2.

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1800.  Two weeks later, appears a comical letter from “An Old Rat-catcher” to “William Duane, Rat-catcher to their Majesties the People of the U.S.”

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1800.  We could tell some curious things of this federal Rat [Kittera].—Id., Aug. 5.

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1800.  A great big Rat, John Lawrence, Esq., has resigned his seat as a senator from New-York in the Senate of the U.S.—Id., Aug. 22.

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1800.  John Reed of Mass. is labelled as “Another, and a Black Rat.”Id., Sept. 5.

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1800.  “Register of Rats Augmented” by 14 names.—Id., Oct. 7.

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1800.  “Another Voracious Rat.”—Heading of a short article concerning Oliver Wolcott.—Id., Nov. 28.

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1800.  

        Register of Rats Augmented.
Rats thrown Over Board.
About to jump Overboard.
Id., Dec. 16.    

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[1812.  I think the old hulk [England] in which you are is near her wreck, and that, like a prudent rat, you should escape in time.—Tho. Jefferson to Jas. Maury, April 25, from Monticello].

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1826.  It revived very strongly the recollection of the “ratting” (as the English phrase it) among the “minority-men,” some twelve or fourteen years ago.—John Randolph to Dr. Brockenbrough, Jan. 6: H. A. Garland, ‘Life,’ ii. 263 (1851).

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