Taiwan Defense Act This bill requires, no later than April 30 every year, beginning in 2021 and ending in 2026, the Department of Defense (DOD) to submit to Congress a report on the progress of DOD with respect to improving the ability of the U.S. Armed Forces to conduct combined joint operations to deny the ability of China to execute a fait accompli against Taiwan. The bill defines fait accompli as the strategy of China designed to allow it to use military force to seize control of Taiwan before the U.S. Armed Forces are able to respond effectively, while simultaneously deterring an effective combined joint response by the Armed Forces by convincing the United States that mounting such a response would be prohibitively difficult or costly.