Donald Trump is running for the Republican presidential nomination, but sometimes it’s hard to tell. On national security the businessman often sounds closer to Bernie Sanders than he does to the GOP policy of active global leadership that has prevailed since the 1950s.

Mr. Trump’s latest walk on the wild left side is his attempt to rewrite the history of 9/11. In his campaign against Jeb Bush, the New Yorker is blaming George W. Bush because the hijackers struck during his Presidency. “The World Trade Center came down during...