A single drug, Sovaldi, started a debate over drug prices in 2014, and now the Alzheimer’s drug Aduhelm might help Congress regain a grip on drug pricing legislation just as it was slipping away. But a lot is up in the air; key congressional Democrats are considering adding Medicare price negotiation to the president’s American Families Plan and passing it with a party-line vote, but the odds are long on that happening. The plan is to first strike a bipartisan...