I once had an English teacher who told me that using profanity excessively frequently indicates that the speaker has a limited vocabulary and is futilely trying to compensate. I think politicians invoking Hitler when talking about those that oppose him or her is analogous.
Much like profanity, invoking Hitler should only be one sparingly and only when warranted. Furthermore, absent condoning genocide, I can't really think of any situation where comparing a colleague, for any reason, to Hitler is warranted. Doing so only minimizes the atrocities Hitler committed.
Senator Rick Santorum (R-PA) appears to have agreed with me at one point. In March, Santorum criticized Robert Byrd's (D-W.Va.) remarks comparing the Senate GOP to Hitler's Nazi, saying the Nazi references "lessen the credibility of the senator and the decorum of the Senate."
However, Santorum recently became the latest politician to invoke Hitler's ghost. Thursday, Santorum said that Democratic
protests over Republican efforts to ensure confirmation votes would be
like the Nazi dictator seizing Paris and then saying: "I'm in Paris.
How dare you invade me? How dare you bomb my city? It's mine."
Santorum has subsequently apologized saying, "Referencing Hitler was meant to dramatize the principle of an argument, not to characterize my Democratic colleagues." Unfortunately, the credibility of Santorum's own words is diminished, as is the Senate's already waning decorum.