I am noting that once again Ms Clinton is reaching 'into African American-related heritage to make her point. Like 'It Takes a Village...'
I also don't think her analogy is terribly far off the mark, if at all.
Washington, D.C. itself is, in fact, constructed on the plantation model. The city is a separate political entity controlled entirely at the discretion of the U.S. Congress, without active representation in the business of the nation.
In its original construction, the residents quarters ran up to immediate juxtaposition with the primary resident of the government.
Those residents were enslaved by law until it became a glaring contradiction to the duplicitous intent of the impending proclamation regarding slaves resident in jurisdictions controlled by the United States.
Slavery was outlaw in the summer of 1862. Had that not been done, they would have remained enslaved as did all others living in jurisdictions controlled by The Union.