So far in 2025, investment-grade bonds have generally delivered modest gains, but municipal bonds have bucked the trend with disappointing performance. The iShares Core U.S. Aggregate Bond ETF (AGG) returned 2.85% through mid-June, while the iShares National Muni Bond ETF (MUB) declined by 1.29%, despite their similar credit quality and low fees. 

One key difference lies in liquidity: municipal bonds are often held long-term, making them harder to trade, with wide bid-ask spreads that erode value during redemptions. Outflows from MUB and uncertainty around tax policy, especially the fate of the 2017 tax cuts, may also be pressuring muni prices. 

For investors in high tax brackets, limited allocations to diversified, low-cost muni funds may still be warranted, but caution is advised, and exposure should generally stay under 20% of fixed income holdings.

Finsum: Structural issues, like the possibility of reduced federal funding for states and large unfunded liabilities, further cloud the muni bond outlook.