E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
One engaged in log-rolling, that is (metaphorically) in furthering anothers schemes or fads; persons who laud a friend to promote the sale of his books, etc. The allusion is to neighbours who assist a new settler to roll away the logs of his clearing.
The members [of Congress] . make a compact by which each aids the other. This is logrolling.Bryce: Commonwealth, vol. ii. part iii. chap. lxvii. page 125 (1889).