Responding to a request for background. The U.S. Congress can change the size of the Supreme Court (the highest court in the U.S.), allowing the President to fill the new vacancies with justices whose ideology aligns with that President, thus shifting the balance. This is known as "packing the court". The size of the court changed through the 1800's as the country grew, but hasn't changed since 1869 when it was reduced to nine. An attempt to increase it to 15 in 1937 failed. These justices serve lifetime appointments.