This claim will be true if a manned (i.e. with human personnel) spacecraft flying under the U.S. flag successfully touches down on an extraterrestrial body no later than December 31, 2020.
'Successful' here means that all crew members survive for at least 24h after the landing or die of causes unrelated to the functioning of the spacecraft. 'Flying under the U.S. flag' means that the spacecraft is either piloted by a U.S. citizen or for the largest part paid for by U.S. institutions. The event must be reported on by CNN and BBC or two equivalently trustworthy news sources.
Background: In January 2004 U.S. President George W. Bush unveiled a new plan for space exploration, starting with a return to the moon by 2020.
Newer estimates by NASA put the date for a human touchdown on the moon into the year 2018.(See http://www.cnn.com/2005/TECH/space/09/15/nasa.moon/index.html)