Their filibuster-proof Senate majority gone, Obama and Democratic congressional leaders opted to pass Obamacare with the help of a maneuver known as “reconciliation.” The risk of a Republican Senate filibuster ruled out the usual House-Senate conference, which might have fixed the ambiguity about state and federal exchanges.

Hence the IRS’s interpretive patch. And hence Halbig, which, like previous Obamacare litigation, shows the power of the courts, in combination with the states — 36 of which opted out of the Obamacare exchanges, and 24 of which haven’t expanded Medicaid — to complicate plans hatched in Washington.

Republican opposition to Obamacare may be hypocritical, irrational and opportunistic — especially GOP opposition to the exchanges, which the party previously favored in various forms. And, yes, the modern filibuster takes counter-majoritarianism to an extreme even the Framers probably didn’t contemplate.

But the Constitution lets the Senate write its own rules.