If I remember correctly, the one area that can’t be altered by amendment to the Constitution is that each state is entitled to two senators. If he wants to get rid of the Senate as it now stands (each state is equally represented) you have to get rid of the whole Constitution.
Article V says that if a state is to be deprived of equal representative in the Senate, it must approve. This means that if California wants 5 senators while every other state gets two, then all 50 states would have to ratify, not just 38. Any amendment changing equal representation must have unanimous consent of the states to enter the Constitution.