trai·tor

[trey-ter] Show IPA
–noun
1.
a person who betrays another, a cause, or any trust.
2. a person who commits treason by betraying his or her country. 

Reagan betrayed our great country by selling arms to Iran.
Another excellent example of "The enemy of my enemy is my friend... until next year, when HE becomes my new enemy."

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SGT. JIRI TREBISSKY H&D SAS

"When the winds of change blow, some people
build walls and others build windmills."
~ Chinese proverb