Protecting Americans with Preexisting Conditions Act of 2019 (Sec. 3) This bill nullifies guidance from the Department of the Treasury and the Department of Health and Human Services titled State Relief and Empowerment Waivers , published on October 24, 2018. The guidance pertains to Section 1332 waivers (also known as State Innovation Waivers or State Relief and Empowerment Waivers), which allow states to forego certain requirements of the Patient Protection and Affordable Care Act in order to implement experimental plans for health care coverage, as long as the resulting coverage meets certain statutory criteria. The guidance, which supersedes earlier guidance from 2015, alters agency interpretation of how states may satisfy the statutory criteria for waiver approval. For example, the guidance (1) redefines acceptable coverage under such waivers to include short-term, limited-duration insurance and association health plans; (2) allows the comprehensiveness and affordability of coverage under such waivers to be assessed based on projected availability, rather than enrollment; and (3) allows the level of coverage to be assessed based on the effects over the entire course of the waiver, rather than per year. (Sec. 4) The Government Accountability Office must report on the number of individuals that would have been expected to lose access to health insurance coverage, as well as the expected effect on mental health care treatment, in the absence of this bill.