That is the first definition of "treason," according to the Oxford English Dictionary. (Sorry it's not linkable.)
Obama supporters who express outrage over the use of the word "treason" seem to think the word means nothing but to the crime defined in law — as if the woman Romney talked to wanted Obama tried and executed.
It's as if people who say "property is theft" are freakishly insisting that property owners be prosecuted for larceny.
Think of all the words we use that have more specific legal meanings that do not apply: This job is murder... The rape of the land... Slave to love...