President Trump’s new push to ditch the Affordable Care Act would throw out a key component of his separate effort to stanch rising drug prices, by eliminating the pathway to approving cheaper versions of some of the most expensive drugs on the market.

Nestled within the 900-or-so pages of the ACA is the Biologics Price Competition and Innovation Act. It lets pharmaceutical companies submit drug applications for products that mimic expensive, complicated drugs called biologics without having to jump...