Donald Trump’s increasingly grotesque behavior is not just the defining aspect of his presidential campaign, it’s an ongoing test of character for the elected Republicans who have endorsed him.

The stakes of that test reached a new plateau when Trump attacked the family of a Muslim American soldier killed in Iraq, after his parents’ appearance at the Democratic convention. Khizr Khan’s Thursday speech has, somewhat unexpectedly, become the most iconic moment of either convention, his searing indictment of Trump—“you have sacrificed nothing, and no one”—compared to the immortal words that helped unravel McCarthyism: “Have you no sense of decency, sir?”

Trump’s response was an offensive non-sequitur intended to degrade and dismiss his victims and enemies. In interviews with The New York Times and ABC News, he mocked Khan’s faith with the suggestion that Khan had forbidden his wife, who stood silently by his side on the stage, from speaking in public. This was horrifying enough, but the thing that made it vintage Trump was that it was premised on a lie. After the convention, but before Trump had gone on the attack, Ghazala Khan had spoken freely, through incredible grief, in an interview with MSNBC. “I told him, ‘don’t be a hero, go safely and come back as my son.’ He came back as a hero.”

The reaction from Trump’s GOP enablers tracked their statements about nearly every Trump controversy. As usual, electorally vulnerable Republicans condemned Trump unequivocally, while party leaders like Mitch McConnell and Paul Ryan contradicted his words only, as if they’d been uttered by a disembodied voice, rather than by the standard bearer of their party. None of them revised their view that Trump should be the next president.

This weak-kneed response surprises and disappoints all manner of opinion makers and anti-Trump Republicans. But the real surprise will come if, in the midst of a closely contested election, Trump’s chief party backers ever experience an epiphany and rescind their endorsements. As stipulated above, this is a test, but it’s one we’ve seen before, and the results are a disaster for those hoping Ryan and McConnell will begin to exhibit daring leadership.