Alyssa Rosenberg writes The Post’s Act Four blog about politics and culture.

If you’d designed her in a lab, you could not have produced a more highly optimized first daughter than Ivanka Trump. Her wardrobe is stylish but not risky. She’s an Instagram-worthy mother of three young children. She works, but for her father, recasting ambition as fidelity to family. When her father was elected president, Trump disavowed any intention of joining his administration, insisting demurely, “I’m going to be a daughter.” Five months later, she has a West Wing office and an official title, but only so she could give her “critics the comfort that I’m holding myself to that highest ethical standard.”

Perhaps because of chromosomal coincidence — the Trump administration and the three preceding it have had a total of seven daughters and just three sons — there’s something of a Cult of the First Daughter in American politics. From Margaret Truman to Chelsea Clinton to Malia and Sasha Obama, the first daughter has captured the national imagination. She is a potent cultural symbol: a princess in a country that threw off kings yet swoons over royalty; the object of chaste affection in teen comedies; proof of her father’s capacity for tenderness.

Like Julie Nixon Eisenhower, whom Nora Ephron once described as “the only woman in America over the age of twenty who still thinks her father is exactly what she thought he was when she was six,” Ivanka Trump is her father’s defender. Like Margaret Truman, she brings out the protective instinct in her presidential father — except Harry threatened to punch out a critic who panned Margaret’s singing, while Donald Trump grumbles about threats to Ivanka’s licensing deals.

Donald Trump’s response to Nordstrom’s decision to drop his daughter’s line — “She’s a great person—always pushing me to do the right thing!” he tweeted — illustrates the ambitious way the family has revamped and expanded the first daughter’s role.

(Gillian Brockell/The Washington Post)

Ivanka Trump herself is attempting an audacious double act, proclaiming her loyalty to her father even as she hints to the public that she, too, sees the flaws in his character and policies. Unlike her predecessors, she is not the innocent victim of attention and anger thrust upon her as a consequence of her father’s career. Ivanka Trump is a canny operator seizing a rare opportunity to build a dynasty — or at least a brand — and using the Cult of the First Daughter to do it.

In this dynamic, Donald Trump gets the same benefits from his daughter that Richard Nixon got from Julie Nixon Eisenhower when she defended her father’s reputation during the Watergate crisis. Both daughters served as important validators for their fathers — Julie for Nixon’s political integrity, Ivanka for Trump’s sexual conduct. After a leaked tape revealed Donald Trump discussing grabbing women without their consent, Ivanka Trump described his comments as “clearly inappropriate and offensive,” then pivoted to vouch for him: “The greatest comfort I have is the fact that I know my father.”

But if Julie Nixon Eisenhower dutifully barnstormed in service of a lie about her father’s honesty, Ivanka Trump has been able to turn her defense of her father into a branding exercise. Her latest volume, “Women Who Work,” comes out on May 2. Her ability to manage her father bolsters her credibility as a guide for young women entering workplaces where at least some men still think, talk and act like him.

However well this scenario serves the Trumps, it’s distasteful to watch a grown woman wheedling her father for policy changes as if they were treats or a credit card for a younger half-sister. On the campaign trail in September, Trump claimed to have adopted a child-care policy because Ivanka told him: “Daddy, Daddy, we have to do this.”

This style reduces important issues, from gay rights to climate change, to girlish whims, as if family benefits and the fate of the planet are as trivial as the choice of centerpieces at a wedding or a flashy sports car bestowed as a sweet 16 gift. Their preservation or destruction becomes a matter of Trump’s fatherly magnanimity, rather than a statement of national significance.

This dynamic sets us up as supplicants to the supplicant in chief: Donald Trump won’t listen to us, but maybe he’ll listen to her. It also allows Ivanka Trump to amass power and official status that far exceeds that of Luci Baines Johnson or Julie Nixon Eisenhower even while shrugging off responsibility.

For Ivanka Trump’s purposes, it’s fine if she fails in her attempts to sway her father. Her role in the administration is to be the person who listens politely to Planned Parenthood or Al Gore, rather than to actually negotiate peace in the Middle East or halt the opioid epidemic, to name two of her husband’s tasks. It’s to be well-bred and well-intentioned.

Being the person who soothes and coaxes her father, but who can’t change his essential nature, is a way of insulating Ivanka Trump from criticism — thus bolstering her book sales and lifestyle brand. “I don’t know what it means to be complicit,” Trump told CBS’s Gayle King in an interview this last week. Maybe she’s right: You can only be complicit in someone else’s game, not your own.