Rep. Jim Himes (D-Conn.) said Sunday that a White House insider is warning President Trump of a “massive market reaction” if he fires Federal Reserve Chair Jerome Powell. “I mean, what happens if there’s a tweet that says the Fed chair is gone?

Undermining that independence for the sake of one man’s political agenda won’t just spark academic debate—it will raise your mortgage, inflate your grocery bill, and destabilize financial markets.

Some $2.5 billion in renovations to the central bank’s headquarters in Washington have put Powell in the hot seat over management of the project, which has cost about $600 million more than initially...