Virginia’s first lady needed a designer dress for her husband’s inauguration.

When a political patron offered to buy her an Oscar de la Renta gown, fit for ladies who lunch or a Vogue cover shoot, Maureen McDonnell jumped, according to federal prosecutors, until an aide to her husband, Gov. Bob McDonnell, vetoed the gift. Ms. McDonnell sent off an angry email: “We are broke, have an unconscionable amount in credit card debt already, and this Inaugural is killing us!!”

In most tales of political careers destroyed by personal weaknesses, it is the officeholder’s spouse who has wound up embarrassed and humiliated. The wives of two former governors, Eliot Spitzer of New York and Mark Sanford of South Carolina, and of former Representative Anthony Weiner of New York, have often looked like stunned bystanders to their husbands’ sex scandals. The archetype has inspired a television drama, “The Good Wife.”

But there is another drama that plays out, too: the political spouse whose own misjudgment and taste for luxury contribute to an officeholder’s downfall.

In a 43-page federal indictment of the McDonnells, charging them with aiding a Virginia businessman in exchange for cash and designer baubles, prosecutors portray Ms. McDonnell as the person whose desires for luxury items led the couple to use the governor’s office to promote a contributor’s dietary supplement business.