Please visit the U.S. Embassy Lisbon COVID 19 page for the most recent information: https://pt.usembassy.gov/covid-19-information/
The Government of Portugal extended current travel restrictions on non-essential travel (tourism) through June 30, 2020.
Exceptions to the travel restrictions include entry, transit, and exit of Portuguese nationals or third country nationals who have a valid residence permit or long-term visa.
For clarification on eligibility for transit, entry or exit requirements, contact the Portuguese Embassy or nearest Portuguese Consulate in the U.S., or follow the Portuguese Immigration website (FAQ in English) https://imigrante.sef.pt/en/covid-19/faqs/#1585841681080-ba44aa0a-04fc