It is not necessary to have a justice appointed if Stevens retires. At that moment we will have 4 conservative justices, one wishy washy justice (Kennedy) and 3 liberals. We will have a conservative court the moment he retires with or without a successor being named. This is so because most of the circuits are already conservative and there will be insufficient liberals votes (even should wishy washy Kennedy vote with the liberals) to overturn those conservative decisions. If the president is denied the approval of his new appointment by filibuster then the republicans can use the same method on any future appointments by succeeding democrat presidents, keeping the conservative court indefinitely. Hopefully in the future we can keep at least 41 conservatives in the senate who will oppose liberal appointments.
I should of read further. Take a look at my Post #57. I'm just curious how long that can go on, under the Constitution. Blackbird.