Although Democratic presidential candidate Bernie Sanders has positioned himself as a more liberal alternative to Hillary Clinton, he stands on the conservative side of one key issue: gun control. In 2005, Sanders voted for the Protection of Lawful Commerce in Arms Act, a terrible law that shields gun sellers and manufacturers from legal liability in most lawsuits. Before the PLCAA, many states allowed victims of gun violence to sue gun sellers who negligently entrusted potentially dangerous individuals with firearms and ammunition. The law effectively nullified the majority of these state protections. Clinton voted against it. Sanders has continued to defend it.

Given this stark distinction, you might expect Sanders to prepare a strong defense when questioned about his record on guns. Instead, when the topic arose during Tuesday’s Las Vegas debate, Sanders fumbled, raising his typical retort that he represents a gun-friendly state but supports gun control elsewhere.

This answer is pretty much the worst one Sanders could possibly provide. By alleging that urban areas need stricter gun laws than rural ones, the senator adds an awkward racial undertone to the gun debate. Vermont—which, Sanders claims, can handle loose gun restrictions—is 1 percent black. Baltimore—which Sanders has cited as an area in need of stricter gun control—is about 64 percent black. It’s alarmingly easy to read Sanders’ rejoinder here as an implication that rural whites can be trusted with guns and urban blacks cannot be.

What’s worse, Sanders’ defense of his pro-gun votes doesn’t actually make any sense. The PLCAA did not only protect gun sellers in Vermont. It protected gun sellers in every state in America. Thanks to the PLCAA, it doesn’t matter whether a gun store negligently sells 4,000 rounds of ammunition to a lunatic in Vermont or Maryland. The store is protected from a lawsuit thanks to the law Sanders still supports.

Sensing Sanders’ weakness on guns, Martin O’Malley dove into a horror story out of Colorado, claiming that the PLCAA barred the family of an Aurora victim from suing the supplier who sold James Holmes his ammunition. That story is true. Sanders owes his supporters a good explanation for why he thinks that family did not deserve justice. He didn’t give it on Tuesday night.

Read more of Slate’s coverage of the Democratic primary.