Republican presidential candidate Carly Fiorina with her husband Frank Fiorina at the Republican presidential primary debates at the Reagan Library on September 16, 2015 in Simi Valley, California. (Photo by Justin Sullivan/Getty Images)
Betty Boyd Caroli is author of the forthcoming "Lady Bird and Lyndon: The Hidden Story of a Marriage That Made a President."

When Bill Clinton famously said that if you elected him, you’d get “two for the price of one” — a nod to Hillary Clinton’s political acumen — it delighted some and outraged others.

Why?

Perhaps because he spoke more directly than usual about a reality history has already taught us: Even though voters know from their own experience that a wife or husband often plays a key role in the spouse’s career, we often don’t pay enough attention to this dynamic during presidential elections. Relatively few questions are asked on the campaign trail about the candidate’s own partnership at home.

Contrary to the perception that activist figures like Eleanor Roosevelt or Mrs. Clinton were outliers, and that the role of other contemporary first ladies has been primarily ceremonial — if not derided outright as being that of a “traditional Stepford booster” — first ladies have had a substantial impact on their husbands’ presidencies. Nancy Reagan’s “My Turn” shed light on the reasons she insisted on maintaining veto power over President Reagan’s schedule. Rosalynn Carter’s “First Lady From Plains” revealed the part she played in the Camp David talks. But we didn’t learn about the contributions they’d made until after their White House tours ended. Ideally, we’d learn as much as we can about them before casting our votes.

A particularly useful example is that of Lady Byrd Johnson. I grossly underestimated her almost thirty years ago when I wrote “First Ladies” and echoed the accepted view at the time: that she was a shy bystander to a politically gifted husband, Lyndon Baines Johnson. But more recently opened records at the LBJ presidential library yield evidence of a decisive, activist teammate who held an important advisory role in her husband’s career.

The courtship letters she and Lyndon exchanged in 1934 show an ambitious, strong-willed young woman who liked “to argue about economics and religions.” Mrs. Johnson’s diary, eventually opened to the public, describes how she shrewdly identified certain legislators for extra attention before crucial votes.

In contrast to Jacqueline Kennedy, who would privately refer to women in the press corps as “harpies,” Mrs. Johnson went out of her way to invite women journalists upstairs at the White House for tea and worked to build relationships in service of getting the best possible coverage for her husband — and herself.

In 1964, when Democrats gathered in Atlantic City to nominate their candidate for the upcoming presidential election, President Johnson, despondent about how his time in the Oval Office was going, initially vowed to turn down the party’s nomination to run for a full term, protesting to advisors that Democrats really “don’t want me anyway.”

Aides couldn’t sway him, but according to Mrs. Johnson own accounts, it was she who stepped in to reassure the president that he was worthy, and that to drop out would effectively hand victory to his foes. We know now, of course, that he went to the convention, where he accepted his party’s nomination and then won the general election by a landslide.

In general, staff members have recounted, no one worked long for President Johnson without receiving his two-word answer to questions about how to proceed, in a variety of situations: “Ask Bird.”

He sought her counsel during a difficult episode, when one of his close advisors, Walter Jenkins, was arrested at a YMCA along with another man on a sex charge. Mrs. Johnson urged LBJ to issue a “gesture of support” for Jenkins, but the president was wary about making any public announcement. She issued her own sympathetic public statement about Jenkins, saying, in part:

“My heart is aching today for someone who has reached the end point of exhaustion in dedicated service to his country. Walter Jenkins has been carrying incredible hours and burdens since President Kennedy’s assassination. He is now receiving the medical attention which he needs. I know our family — and all of our friends — and I hope all others — pray for his recovery.”

It’s no wonder a woman like that became invaluable to a husband whose well-known brashness easily upset associates and alienated people he needed as allies. Mrs. Johnson’s genius was seeing her husband clearly for who he was, and that her function in their power dynamic was to smooth out the wrinkles he made and mend the breaks he caused.

Above and beyond smoothing ruffled feathers, over the course of their relationship, she consciously eschewed confrontation with the women with whom LBJ was said to have had affairs. When I talk to women now, this is the aspect of Lady Bird’s role that’s hardest for most to reconcile. She did so, though, I believe, because she accepted that his reported infidelities were part of his need for constant admiration — and thus ultimately part of helping him succeed.

In one of his courtship letters, entreating Lady Bird to marry him, LBJ recounted an evening spent with his “little radio writer friend,” with whom he’d dined and then “talked — just talked” “until late.” In an interview years later, Mrs. Johnson candidly noted that while the relationship between LBJ and the radio writer was not platonic, it had served a purpose — she “sharpened him up” intellectually and socially.

Mrs. Johnson was extraordinarily pragmatic in the way she dealt with infidelity. After LBJ’s death, she even extended a not-so-sincere invitation to one of his rumored mistresses to visit the Johnson ranch.

Adding it all up — Lady Bird’s behind-the-scenes political savvy, her stabilizing power with her husband and within his inner circle — the typical helpmate or booster labels are inadequate. She was a pivotal player in what she sometimes referred to as “our presidency.” And as the Atlantic’s Scarlet Neath reported last year, assessing the impact of first ladies on presidencies, the question Mrs. Johnson asked and put down in her diary — defining, really, how she saw herself and her position — was: “What shall I interest myself in and how much?”

Something for voters to keep in mind this election season.

With twenty-plus candidates and their spouses seeking the White House, Americans would do well to have a better understanding of who the potential future first ladies and gentlemen are. Does Columba Bush advise Jeb? Would Jane Sanders speak publicly on controversial issues? How would Frank Fiorina fit in as America’s first first gentleman? And is Bill Clinton prepared to offer another two-for-one deal? At a time when voters are demanding that politicians offer straight talk, isn’t it time to drop the campaign-trail pretense that spouses are a mostly insignificant backdrop? The next barrier-breaking moment may just be the moment when candidates ‘fess up to what voters already know: spouses can be crucial to a president’s success.