AIPAC money, he also beat a MAGA adjacent guy in 2022 gubernational race so I think it's reasonable to say he sews up PA (even with a lukewarm approval rating in the state)
He's a good nice resume if we're talking about "mainstream" issues (reproductive rights). And he's nothing if not seasoned, one of those guys that at the very least is not camera shy, timid or erratic. You're getting somebody who is ready for primetime, as opposed to say Mark Kelly, who strikes me as having much less media training/ interest in "the game".
For the record, Shapiro is not my pick. I just think he's a guy that's ready for the national stage, and smokes Couchboy and Trump for that matter from a debate/ soundbyte perspective. I'm also a PA resident and think he's got enough clout here to carry the state easily (though, we'll likely be blue with or without him)