Stablecoin giant Circle announced on Thursday that Heath Tarbert, a former regulator who has held senior positions at Citadel Securities and the World Bank, is joining the company as Chief Legal Officer and Head of Corporate Affairs. The appointment comes at a critical time for Circle, which oversees nearly $30 billion of the USDC stablecoin along with Coinbase, but is navigating U.S. regulatory waters that have become deeply hostile to crypto. As a former Chairman of the Commodity Futures Trading Commission—an agency that is jockeying for a bigger role overseeing crypto markets—Tarbert is likely to provide Circle with both expertise…