Conflict in the Democratic Party over Israel has long revolved around symbolic issues, such as the drama around how many elected officials would show up to Prime Minister Binyamin Netanyahu's speech to Congress earlier this month. A primary in Maryland for an open Senate seat could now bring many of these tensions out into the open.

The impending retirement of the stalwart Democrat Barbara Mikulski means Maryland has only its second open Senate seat in three decades. There is no clear successor. 

So far, two Democratic members of Congress from suburban Washington, Chris Van Hollen and Donna Edwards, have announced their candidacy. Both have very liberal records and are well liked by progressive groups. However, there is one distinct policy difference between the two of them: their views on US policy in the Middle East. And this difference could doom Edwards on election day.