Just before going on with the Liberty Prime attack on the purifier, I did part of the Head of State quest, killing the slavers at the Lincoln Memorial and setting the slaves from the Temple of the Union on their way.
I know they take a couple of days to get to the Memorial, so in order to "kill time" I completed the Take It Back! quest in the meanwhile...
I have Broken Steel installed, so I can continue playing, but when I go to the Memorial, the slaves are not there yet, even though a couple of weeks are supposed to have passed.
Is there any way to complete the Head of State quest?