Isn't this the problem? Every President gives Nasa a new set of priorities, which they work on for a while until the next President comes along and changes things again. Back in 2004, George W Bush was also announcing a return to the Moon:
"Our third goal is to return to the moon by 2020, as the launching point for missions beyond. Beginning no later than 2008, we will send a series of robotic missions to the lunar surface to research and prepare for future human exploration. Using the Crew Exploration Vehicle, we will undertake extended human missions to the moon as early as 2015, with the goal of living and working there for increasingly extended periods. "
Jan 14, 2004 - https://history.nasa.gov/Bush%20SEP.htm