Captain America's Daughter Was Worthy of Mjolnir 20 Years Before Endgame
The moment when Captain America lifts Thor's hammer Mjolnir in Avengers: Endgame had theater audiences cheering, but comic fans saw Cap's daughter accomplish the same thing 20 years earlier. The Marvel Comics series What If…? has always been a place to throw just about any narrative concept at the wall. Such was the case in the 1998 story "Secret Wars: 25 Years Later" from What If...? #114 by Jay Faerber and Gregg Schigiel, which shook up a medley of popular Marvel heroes in a baby-making blender and composed a team from their offspring. Some of these pairings made more sense than others, and the oddest had to be the union between Steve Rogers and Rogue of the X-Men, whose daughter Sarah, a.k.a “Crusader”, proved worthy of lifting Mjolnir decades before the Russo Brothers had her father do it in Avengers: Endgame.
The conceit of the story is pretty simple: Victor Von Doom has a rebellious young son called Malefactor, whose ambition overleaps itself and sets him down a power-hungry path of domination. This leads him afoul of the proto-Young Avengers group that includes his half-brother Balder, the somewhat insecure son of Thor. Their climactic confrontation seems one-sided until a familiar weapon comes hurtling through the walls of Castle Doom and returns to the hand of Sarah Rogers, who stands proudly wielding Mjolnir when Balder could not. But before she gets a chance to use it, Doctor Doom returns and teleports his disobedient child away.
Precisely what determines “worthiness” as Mjolnir’s prerequisite for being moved has long been a subject of debate among comic fans and even characters themselves. The Uru hammer was originally created by Odin’s demand as a housing unit for the God Tempest, and in its rawness was almost too powerful for even Odin to wield. Therefore one of the primary purposes of its enchantment is to ensure all of that power doesn’t fall into incorrect hands. But after The War of the Realms, Thor himself learned that the pursuit of worthiness is, in itself, what makes one worthy.
Even though this What If...? takes place years before that event was written, perhaps that is why Balder can’t lift the hammer. He isn’t concerned about being worthy to lift Mjolnir, he is concerned about being worthy of his father’s legacy. Those are two very different goals. Sarah Rogers, on the other hand, is presumably able to lift it because of the purity of her intentions: to save her friend and protect the planet. And it probably helps that she isn’t overthinking it.
There's also the matter of Sarah’s mother Rogue. Setting aside that Steve calls her “Carol,” indicating that he married Carol Danvers in Rogue’s body, it’s not out of the question that Sarah’s inherited absorption powers could play a role in why she is able to wield the hammer—especially if that ability is at all genetic to Thor, which would mean it could be passed down. After all, Tony Stark theorizes in Age of Ultron that Mjolnir’s handle is essentially hardwired to his handprint. Given that we’ve since seen Captain America operate it with surgical precision, that comment is more than likely Stark assuaging his bruised ego. But one can only imagine how he would’ve reacted to a teenage girl getting to use Mjolnir before he did.