(idiomatic) As an opener, a sometimes sarcastic indicator to indicate a past event being mentioned is particularly important.
Origin of four-score-and-seven-years-ago
In Abraham Lincoln's Gettysburg Address, he used this (at the time) commonplace measure of score, meaning "20 years". In modern language, it would be simply "87 years ago". However, the widespread notoriety of Lincoln's address, the unusual wording and its status as the first words of the speech have caused the phrase to enter the public consciousness.