Stocks and Bonds Haven’t Rallied Like This Since 1998

Stocks and bonds are staging an extraordinary run, on track for their biggest simultaneous gains in more than two decades.

Heading into the final two weeks of 2019, the S&P 500 has soared 28.5%, while a bond rally has pushed the yield on the benchmark 10-year Treasury note down more than three quarters of a percentage point.

If the gains…