The first day of the Senate Foreign Relations Committee’s hearings on the legal structure by which US nuclear attacks are to be ordered saw retired Gen. Robert Kehler, a former Stratcom commander, who said he would’ve rejected orders regarding nuclear strikes that he believed were illegal.

Kehler said that if a president had ordered a nuclear first strike he’d have believed it didn’t meet proportionality requirements under international law, and refused to proceed. When asked what would happen after that, he admitted he wasn’t sure.

Gen. Kehler said it was an interesting question, however, as while the military is obliged to follow a president’s orders, they are not obliged to follow illegal orders, saying the Stratcom commander always keeps legal advisers on hand, and would be obliged to not follow illegal orders.

So far this has been a purely hypothetical case, but many in Congress, including Sen. Bob Corker (R-TN) are concerned President Trump’s attitude toward North Korea has raised concerns he might try to order a nuclear attack, and that discussion of the legality of such a possibility was long overdue.

The US has long refused to officially rule out the option of a nuclear first-strike in war. President Obama was said to have considered such an effort, but he was advised against it on the grounds it would make him “look weak.”