The Constrained Constitution and the SALT Deduction

Yesterday, the 2nd Circuit rejected several states' challenge to the elimination of the "SALT" (State and Local Tax) deduction from federal income taxes (basically, allowing you to deduct state tax payments from your federal income). The elimination occurred under the Trump administration, and it was a savvy play -- it mostly affects "blue" states (which tend to have higher state taxes), and it mostly affects wealthy residents of those states (who pay the most in state and local taxes). One would not be wrong to suspect that the former concern predominated over the latter in terms of the Trump administration's logic.

Nonetheless, the Trump administration's potentially venal motives do not themselves make out a constitutional violation, and the Second Circuit here found none. That was so even though, as Jonathan Adler observed, from a purely partisan perspective the states drew a very favorable panel. It didn't matter -- there's no basis in the constitution for why any particular state is entitled to a particular tax regime, so the blue states lose.

I actually am, however, a bit curious as to how conservative legal observers explain this outcome by liberal justices. We often hear that only conservative-style originalism serves to "constrain" judges and prevent them from simply voting their partisan preferences. Yet these judges are not conservatives and, it seems fair to assume, were likely not fans of the Trump administration's gambit here. So what caused them to nonetheless reject the suit? The answer has to be something that constrains liberal judges from merely voting their policy preferences (at least some of the time) -- but the originalist/textualist apologia typically denies that said "something" can exist.