A senior policymaker at the Federal Reserve said Thursday that the central bank should continue to raise interest rates, despite public criticism from President Trump.

“I believe that some further gradual adjustment in the federal funds rate will be appropriate,” said Fed Vice Chairman Richard Clarida, a Trump appointee, though he added that if economic data showed a slowing U.S. economy, then the Fed could aim for fewer rate hikes.

“[A]t this stage in the business cycle, I believe it will be especially important to monitor a wide range of data to continually assess and calibrate the level of the policy rate that is consistent with meeting our objectives on a sustained basis,” said Clarida.

Trump has called the Fed “overly aggressive” in its plan to raise interest rates, though several of the central bank’s key leadership positions have been filled by his nominees.

The Fed lowered interest rates to abnormally low levels as a reaction to the global financial crisis, and raising rates now are seen as a return to normal. Central banks lower interest rates to encourage lending and borrowing to help stimulate the economy in economic downturns, while they raise rates during economic booms to prevent rapid increases in the price of goods and services.