Article II, Section 2, Clause 2 of the US Constitution also known as the Appointments Clause determines that the US President is the one responsible for nominating the justices of the US Supreme Court. The US Senate will have to reject or confirm the nomination later.
The Justices of the US Supreme Court hold office as long as they choose and can only be removed from there by impeachment.
States and the federal government have both exclusive powers and concurrent powers. There is an ongoing negotiation over the balance of power between the two levels.
