(Bloomberg) -- Investors are pouring the most money since September into the riskiest U.S. local debt, a boon to lower-rated issuers such as Puerto Rico that plan to borrow in the $3.7 trillion municipal market in coming weeks.

The cash infusion is leading speculative grade munis to a 2 percent gain to start the year, beating the broader tax-free market and drawing a buy recommendation from Citigroup Inc.

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