Many of the problems with litigation under our federal system, as I’ve noted before, arise when state courts can reach out to project their power onto litigants and disputes outside their borders. Public choice economics suggests that when courts are answerable to the political and legal classes of a single state only–say, California or Montana–they might not be ideally responsive to the interests and due process rights of out-of-state parties who have been compelled by force to show up and defend a lawsuit. Even if state judges and juries manage to avoid the temptation of “home cooking”–dishing out tastier outcomes to down-home litigants and lawyers than to outsiders–there remains the wider problem of forum-shopping, in which–even if no forum intends to act other than impartially–lawyers can bring an action in whichever of multiple available forums is most gainful for their side and unwelcome for their opponent.

A great deal, therefore, hangs on when state courts can compel absent parties to show up and defend a lawsuit. When may a state assert jurisdiction over a distant party even though it lacks one of the relatively uncontroversial grounds for doing so, such as that the events being sued over happened within its borders?

And here there has been good news to report in recent years. Our system relies largely on the federal judiciary to police overreaching by state courts in their jurisdictional claims, and after decades of irresolution, the U.S. Supreme Court has lately been getting much more serious and confident about drawing the right sorts of lines. Importantly, it has done so with support from both liberal and conservative wings of the Court. In the most significant recent case, Daimler AG v. Bauman (2014), Justice Ruth Bader Ginsburg wrote for a unanimous Court, with only Justice Sotomayor writing a separate concurrence. (The case dealt with an international as distinct from interstate claim of jurisdiction, but made precedent for both).

But some states have pushed back against Daimler, which may be why the Court granted review of two cases on which it will hear oral argument tomorrow, April 25. In Bristol-Myers Squibb Co. v. Superior Court, California courts took jurisdiction over hundreds of cases from other states alleging side effects from the drug Plavix, even though the other cases had no particular connection with California other than that their lawyers wanted to convoy them in along with the actual California cases. In BNSF Railway Co. v. Tyrrell, Montana opened its doors to litigation against a railroad based elsewhere over injuries that did not occur within Montana.

It seems unlikely that the Court will declare a change of heart and back off its 2014 near-unanimity. Helpfully, the Trump Justice Department has filed an amicus brief arguing that the California Supreme Court overstepped the line when (over a dissent from three of its members) it found jurisdiction over the out-of-state drug cases. Still, lawyers will be looking at the possibility that some distinctive sub-pattern in one or both of tomorrow’s cases (such as federal law’s recognition of the railroad industry as having a distinctively national workforce) might justify carving out an exception to its rule.

The stronger outcome would be for a united Court to say unambiguously, about its Daimler holding: we said it, and we meant it.