Bitcoin’s 50% plunge from its October peak has done more than just erase $2 trillion in market value — it has reignited a fierce debate over the fiduciary math of the American retirement system. As investors scramble to parse the drivers of the latest crash, industry observers are asking if volatile digital assets have any business being in a $12.5 trillion 401(k) market designed for stability. “If investors want to speculate on crypto, they are welcome to do so on their own. 401ks exist to help people ...