Just their way of paying tribute to John Kerry.
Yes, I was thinking the same thing. I read that the mother and brother of one of the flip-flopping young ladies were mortified and completely embarrassed that their family member showed up at the White House like that. Evidently, flips are a bit a fashion statement right now, as some have rhinestones, etc. and can cost quite a bit, but even the sellers of such footwear have gone public and said ANY kind of flip flops in the WHITE HOUSE are a big NO-NO.