Illinois citizens can just drive to Indiana to buy a gun and bring it back to Illinois. In fact they do...a lot! Illinois can pass a law saying that their citizens can't keep those guns at home or can't walk around with them without a FOID card, subject to the constraints of a conservative Supreme Court. They might be able to place restrictions on those FOID cards (haven't dug into the details of how they work) that say you lose your card if you buy a gun out of state. But in general, the more readily available guns are just across the border the harder it is to keep your citizens from getting them, precisely because they're allowed to cross the border to buy them. That's why national-scale gun laws are important if you really want to do something about gun violence.

The analogy works perfectly for abortion too. The difference is you're not bringing the abortion back from Indiana to Illinois, as it were. What happens in Indiana stays in Indiana. They're trying to find clever ways to get around that with some of those bounty laws, but fundamentally that's the legal argument. Kavanaugh specifically said in his concurrence on Dobbs that interstate travel is permitted and states wouldn't be able to ban this kind of thing, which should've been a clear signal to the states not to try this stuff and to Lankford not to object to the Senate bill. Of course, my faith in Kavanaugh actually sticking to what he said isn't that high and I'm pretty cynical about what the GOP actually has in mind.