Economics of UK-US trade

I would like to come up with a justification in economic theory for mentioning this, but so far I haven't. In reality I just want to complain that, on the week of my first visit to the US in seven years, the pound has fallen to its lowest level against the dollar since 1985.

Aside from the possibility that all 2 million of Tuesday's visitors to Washington came from Britain, exchanging billions of pounds into US currency on the same day, I don't think I can manufacture a connection. Just bad luck. Is there a macroeconomic theory for that?