For many US investors in high income tax brackets, tax-exempt municipal bonds often serve as an important source of income in otherwise taxable accounts. In most normal times, the exemption of municipal bond interest from income tax makes many of these bonds trade at lower yields than similar maturity US treasuries until the after-tax yield / taxable equivalent yields are only slightly higher than treasury yields. In the market crash we have seen so far in 2020, municipal bond funds have seen significant declines in their values, so that even high grade munis have been