A LEO, AN L.E.O.-- A historic, indefinitely
It's a LEO.
It's a historic event. Unless you write with an English accent. "istoric"
Now, I suppose you could make an argument for LEO needing an as the indefinite article, if you were saying "I saw an EL EE OH sleeping in his squad car." But don't you use the acronym for police officer like a word... as in "Leo, the lion?"
So, from now on... A LEO, okay?
And, A historic, too...
Your friendly neighborhood beat (not beet, BTW) Elio
Please... Seeing these oddities gives me facial tics...