The Democratic presidential primary fight is now down to Bernie Sanders and Joe Biden and the outcome will reflect the Party’s true soul on issues like international trade. Thus far, trade has played a lesser role in the election than issues like health care and income inequality. If Mr. Sanders represents the very liberal-socialist wing of the Party, the former Vice President is the moderate wing and he has shown strong support in the past for conventional U.S. free trade policy. Unlike most Democrats in the U.S. Congress, Mr. Biden supported the Trans-Pacific Partnership agreement.  It is unsurprising that Joe Biden won the delegates offered up in southern states this past Tuesday since this is the more conservative region of...