In 1964, the US Republicans nominated for President Barry Goldwater, a right wing senator who wanted, amongst other things,to have the authority to utilise tactical nuclear weapons on the battlefield.
Not surprisingly, this unnerved quite a few people. This was how the Democrats responded. The ad only ran once, but encapsulated the election. The Democrats won by 61%, and this has become the gold standard as to effective political advertising.
Have a look here.