What is "stalking horse"

alt. 1 (context dated English) A horse used as cover by a hunter stalking game, 2 (context idiomatic politics English) A candidate put forward to serve a hidden, ulterior purpose in a political campaign, such as testing the field for another potential candidate by gauge voter sentiment or covertly helping another candidate by attracting voters away from a third candidate. 3 (context idiomatic by extension English) A person, thing, or expedient used in a deceptive manner, to achieve some hidden purpose; a pretext or ruse. n. 1 (context dated English) A horse used as cover by a hunter stalking game, 2 (context idiomatic politics English) A candidate put forward to serve a hidden, ulterior purpose in a political campaign, such as testing the field for another potential candidate by gauge voter sentiment or covertly helping another candidate by attracting voters away from a third candidate. 3 (context idiomatic by extension English) A person, thing, or expedient used in a deceptive manner, to achieve some hidden purpose; a pretext or ruse.

A stalking horse is a figure that tests a concept with someone or mounts a challenge against someone on behalf of an anonymous third party. If the idea proves viable or popular, the anonymous figure can then declare its interest and advance the concept with little risk of failure. If the concept fails, the anonymous party will not be tainted by association with the failed concept and can either drop the idea completely or bide its time and wait until a better moment for launching an attack.