Note to self:
Avoid invoking Hitler in the political realm. Wait
for opposition to bring it up then beat them over
the head with it.
Before attacking somebody for some comment, ask "Is this something I could possibly have said myself?"
I think a lot of people have said something like this at one point or another, in reference to Hitler not using gas against allied troops. We know what Spicer meant, and it's something our parents or grandparents might have said and understood.
In a way, the apology or explanation was worse than the original comment, since the clarification implied that those killed by gas didn't include many who had been German citizens (before they were unjustly stripped of their citizenship by Hitler's Nuremberg Laws).