What just happened to the British pound?

Boris Johnson, that’s what. The mayor of London this weekend came out against Britain’s continued membership in the European Union, becoming the most prominent member of the Conservative Party to buck Prime Minister David Cameron in his efforts to keep Britain in. (Cameron is reportedly “absolutely furious” about Johnson’s rebellion.) The pound fell to its lowest level against the dollar since the bad old days of the financial crisis, over concerns that the country’s leadership has splintered in the face of a so-called “Brexit.”

As the Times helpfully suggests, the debate basically boils down to whether Britain is a stifled global power that has been constrained by its obligations to Europe, or whether it is, in fact, a small island nation that only stands to gain from the economic and military advantages that come from being part of a larger union. While Johnson might deny that Britain is but a husk of its former world-straddling self, his motivations are probably less world-historical than personal: There is much speculation that he sided with the Out campaign because it would put him in a position to lead the Tories should Britain vote Out in a national referendum on June 23.