A group of US lawmakers wants to see cryptocurrency holdings declared at the nation's border – and advocates of the tech are pushing back. Introduced last month, the Combating Money Laundering, Terrorist Financing and Counterfeiting Act of 2017 – which is actually the third iteration of a bill that debuted in 2011 – would bring a range of digital currency services under federal scrutiny, including those that provide transaction mixing services. Yet, the provision that has attracted the particular ire…