In logic, the use of a 'strawman' is an informal fallacy (using it does not mean the proponent is wrong, only that it is unpersuasive). It is very common in political arguments. The user often is either unable or unwilling to attack or refute the argument put forward by their opponent, so he attacks an easier, but less defensible, version setting up a much easier facsimile or strawman to refute.
Although the term is fairly recent (mid 20th C), the concept is well understood in formal logic. Similar terms were used and came from a scarecrow, dummy or effigy standing in for the real thing.
A good example from the Brexit debates is when one person accepts the UK should leave the political union but continue to ensure smooth movement of goods by being part of the Customs Union and SIngle Market, but their opponent's response is to accuse them of refusing to accept the result of the referendum.