Reciprocity Ensures Streamlined Use of Lifesaving Treatments Act of 2020 This bill establishes a reciprocal marketing approval process that allows for the sale of a drug, biological product, or medical device that has not been approved by the Food and Drug Administration (FDA) if the product is approved for sale in another country and there is an unmet need. Specifically, the bill requires the product's sponsor to demonstrate, among other things, that their product has been approved in one of the specified countries, the FDA and listed countries have not withdrawn approval because of safety or effectiveness concerns, and there is a public health or unmet medical need for the product. The FDA may only decline approval if the FDA determines that the product is not safe or effective. The FDA must make such a determination not later than 30 days after receiving a request. Congress may pass a joint resolution to grant reciprocal marketing approval of a product that the FDA declines to approve through the reciprocal process.