“What Iran has done is really highlighted both Bernie Sanders and Joe Biden as representatives of two different poles in the Democratic Party: one a much more hawkish interventionist arm of the party, which used to be dominant, and then Bernie Sanders, representing a more diplomacy-oriented approach, a more collaborative international approach that is ascendant in the party,” said Jeff Weaver, one of Sanders’s top advisers, who went on to ding Biden for the 2002 Iraq vote.

The common assumption about Democratic base politics has been that the domestic trumps the international, that voters in Dubuque would rather hear about how candidates are going to fix their health care than about how they’re going to fix the Middle East.

But that’s not entirely true. Every open Democratic primary since 9/11 has been about war, and the beneficiary of the debate over that issue hasn’t been easy to predict. In 2004, another insurgent Vermonter — Howard Dean — based his entire candidacy on his opposition to Bush’s invasion of Iraq, which was enormously unpopular among Democrats and which John Kerry had voted to authorize. Kerry, after struggling in 2003, when Dean’s antiwar message thrilled liberals and filled stadiums, easily defeated his New England rival when voting began in 2004.