PARIS -- Republican presidential front-runner Donald Trump got into an interesting war of words on Twitter recently with a Saudi prince.
"Dopey Prince (Al-Waleed bin Talal) wants to control our U.S. politicians with daddy's money. Can't do it when I get elected," Mr. Trump tweeted.
Mr. Trump's social-media salvo was truly provocative, and not because he called a billionaire member of the Saudi royal family "dopey." What made Mr. Trump's outburst on Twitter so interesting was his willingness to call out the tacit and longstanding subversion of the U.S. political system by foreign interests.
"You are a disgrace not only to the GOP but to all of...