The CDC requires all air passengers entering the U.S. (including U.S. citizens and Lawful Permanent Residents) to present a negative COVID-19 test, taken within three calendar days of departure or proof of recovery from the virus within the last 90 days.
Singapore has confirmed cases of COVID-19 within its borders. Singapore reverted to Phase Two (Heightened Alert) of its reopening plan as of July 22, 2021, from Phase Three (Heightened Alert), which had been in effect since June 14, 2021.
If you are overseas and your passport expired on or after January 1, 2020, you may be able to use your expired passport to return directly to the United States until December 31, 2021. Click above link for more information.