Jane Sanders calls herself Sen. Bernie Sanders’s longest-serving political adviser and his best friend.

The two met during Mr. Sanders’s first campaign — for mayor of Burlington, Vt., and now Mrs. Sanders is a regular fixture on the campaign trail with her husband. In recent weeks, the candidate for first lady has struck out on her own, hosting her own events with voters and appearing on her own for media interviews.

As voters prepare to make their decision in Iowa, she sat down with WSJ to talk about the past year – and what is coming next for the campaign.