The questions have gotten obsessive: Will she be young or old? Black or white? A campaign asset or a governing ally? A partner or an heir?

Much of the coverage of Joe Biden’s vice-presidential selection process has focused on the specifics of the various contenders, parsing out their records and assets, their potential liabilities, their relationship with the candidate and their fitness for the moment. The hand-wringing over the choice has come to embody what Hillary Clinton once described as “a pernicious double standard aided and abetted by the idea of perfectionism.” All of the women on Biden’s shortlist are smart, qualified, experienced leaders; none of them are perfect.

Which, of course, is true of any Vice Presidential selection. “Joe Biden was not perfect, Paul Ryan was not perfect, Tim Kaine was not perfect,” says Jennifer Lawless, a professor of politics at the University of Virginia. “But perfect is not the bar for men. What we’re seeing this time is anything short of a flawless candidate is a problem.”

But given the stakes of the choice, Democrats are understandably preoccupied with perfection. Biden holds a steady lead over President Donald Trump in both national and battleground-state polls. Putting a woman—and very possibly a Black woman—onto the Democratic ticket is like adding an X factor into what has so far been a stable political equation between two white male candidates. And the way it changes the calculation, whether it helps Biden excite the base or exposes him to attacks he had previously avoided, could reveal the value of X.

There are many good reasons to think X will have a positive value: a woman Vice Presidential candidate is likely to excite the Democratic voters who backed Clinton, elected a record number of women to Congress in 2018, and rooted for the six women contenders in this year’s presidential primary. Biden has suffered from muted enthusiasm among some key demographics groups. Many Democrats say they’ll vote for him but aren’t very excited about it; helping to elect the first woman Vice President could add a jolt of history. “There’s definitely this buzz,” says Stephanie Schriock, executive director of Emily’s List. “Everybody needs a little boost of energy.”

But if X changes the equation, it also reveals why that equation was so stable in the first place. Even though he’s politically similar to Clinton in some ways, Biden’s race and gender have given him some measure of political Teflon. The misogynistic attacks that worked so well against Clinton in 2016 don’t stick to this 77-year-old white grandfather from Scranton. When it comes to landing a hit on Biden, none of Trump’s old tricks seem to be working.

Which means that Biden’s running mate, whoever she is, will immediately become a top target for Trump. After struggling to attack Biden, the Trump campaign has settled on painting him as a “hapless tool of the extreme left.” As soon as his vice presidential pick is announced, they will likely paint Biden as her Trojan Horse. Senior Trump adviser Jason Miller called Biden’s VP his “political living will.”

New research by Lucina Di Meco, a global fellow at the Wilson Center, suggests that social media chatter about women candidates tends to be more negative and more personal than online discussion about male candidates. No wonder, then, that Democrats are trying to find the perfect woman to reduce the target. “They will attempt the racist and sexist attacks against the VP, there’s no doubt,” says Tim Miller, political director of Republican Voters Against Trump. “No matter who the Veep is, they’re not going to have any of those advantages that Biden has. They’re not going to have any of the armor that has protected him, being a moderate white guy, from Trump’s broadsides.”

Already, feminist leaders are bracing for an onslaught. Top women leaders from Emily’s List, NARAL, Time’s Up, Planned Parenthood, Supermajority and the National Women’s Law Center have teamed up to form We Have Her Back. On Friday, they sent a letter to major news organizations warning about “the double standards we’ve seen in the public and media expectations of women leaders,” and asking newsrooms have a “thoughtful conversation internally” about how to avoid perpetuating sexist stereotypes about the vice-presidential pick, including characterizing her ambition, her relationships, and her “likability” in ways that wouldn’t be done for a man.

“If you have kept your eyes open from birth onwards, you would know that major sexism exists, and that it plays out in elections in specific ways,” says Jess Morales Rocketto, a Democratic strategist who signed the We Have Her Back letter. Whoever Biden picks, she says, will be “representative of something, whether or not she wants to be, whether or not she is representative of that herself. I don’t know if anyone can withstand that level of scrutiny.”

Of course, the value of X could be negligible; experts say that the Vice Presidential pick almost never decides the outcome. “Historically they haven’t, and in the ways they have it’s generally if something goes off the rails rather than anything positive,” says David Axelrod, a former top adviser to President Barack Obama. “This notion that a VP candidate is gonna is drive turnout, I don’t buy it.”

And others say that even if Trump blitzes Biden’s running mate with racist and sexist attacks, it’s likely to backfire against the President. “Card-carrying sexists and racists are not voting for Joe Biden anyway,” says Lawless. “And people who are turned off by those kinds of attacks are more likely to say, ‘I’m not standing for that anymore.’”

But no matter she helps Biden or hurts him, X will at least deliver some clarity: she’ll reveal exactly how much a woman can change the equation.

Write to Charlotte Alter at charlotte.alter@time.com.