Wow! Read it again.
In case you still don't get it, Mathews referred specifically to those who spread the Obama as non-American citizen lie. He did not say a single word about people who disagreed with the president.
I know of some folks in Lousiana who call themselves and each other 'crackers'. Is 'cracker' really a perjorative? Or is it a word like 'nigger'? Where you can only safely use it if you are black?