Jerome H. Powell is set to testify as inflation risks are resurfacing, regulatory changes are in flux and the Federal Reserve’s policy independence is in the spotlight.

It’s the first sign of unified opposition for a rudderless and leaderless Democratic Party.

In a letter to the Treasury secretary, the Democratic senator warned against meddling with a system that processes trillions of dollars of transactions.

Robert F. Kennedy Jr. also disclosed that he had reached at least one settlement agreement with a company or individual that has accused him of “misconduct or inappropriate behavior.”

Senators had objected to the financial conflict posed by Robert F. Kennedy Jr.’s decision to retain a financial stake in lawsuits against a major drug company. It remains unclear whether any proceeds would be redirected.

The settlement’s existence after a 2017 accusation had been documented before the defense secretary nominee’s confirmation hearing this month, but the amount had not been known publicly.

President-elect Donald J. Trump’s pick for defense secretary had a more amicable exchange with Joni Ernst, a Republican, who is considered a key vote.