What is the only penalty that can be imposed on someone who is impeached

the penalty is impeachment if the President is breaking the law but the would still get protective services being the president and all

removal from office and disqualification from holding another federal position

Explanation:

The United States Constitution provides that the House of Representatives "shall have the sole Power of Impeachment" (Article I, section 2) and that "the Senate shall have the sole Power to try all Impeachments ...[but] no person shall be convicted without the Concurrence of two-thirds of the Members present" (Article I, section 3). The president, vice president, and all civil officers of the United States can all be subjected to impeachment processes.

The penalty arrived at after the impeachment proceedings can't be forfeiture of life, liberty, or property. According to the United States Constitution, the only penalties allowed are removal from public position and disqualification from holding any other federal position in the future.