What is the origin of the term horse trading?

The term horse trading, which came into usage around 1820, owes its origin to the notorious shrewdness of horse traders who bought and sold horses. As per Macmillan English Dictionary, it means difficult and sometimes dishonest discussions between people who are trying to reach an agreement. In political parlance, it implies any long drawnout negotiation characterised by hard bargaining and compromises. It frequently takes place in democratic institutions like legislative bodies when a parliamentarian or legislator supports some Bill or trust vote in exchange for support for one of his initiatives for another Bill or legislation.