Republicans are talking about "going nuclear" and approving Bush nominated federal judges with a less than 60% majority by simply ignoring the cloture rule that requires that support to overcome a minority filibuster.
The cloture rule is not a matter of constitutional law, and because each House of Congress is the judge of its own procedures, the Courts are probably without authority to overrule even a blatent disregard for Senate rules (not that the conservative leaning federal courts would be inclined to do so). But, if the Republicans take that course, the Democrats should retaliate, by packing the courts when they come into power.
If the Republicans succeed in ignoring the cloture rule to put conservatives on the Court, it wouldn't be the first time that the United States has had a federal judicial branch grossly out of touch with a centrist view of the constitution. Republicans did the same thing prior to the Great Depression which left President Franklin D. Roosevelt facing the Lochner court, named after the 1905 decision (198 U.S. 45) in
Lochner v. New York that the due process clause and freedom of contract rights in the constitution prevented government regulation of employment contracts.
From 1905 to 1934, the court invalidated hundreds of economic regulations of labor, price regulations and restrictions on entering into busienss on similar grounds (relatively liberal Justices Holmes, Brandeis, Stone, Cardozo and Hughes, many now famous in the anals of legal history., were frequent dissenters, obviously not all at once; forgetten Justices Sutherland, Van Devanter, McReynolds and Butler where part of the conservative majority). They threatened to stop the New Deal in its tracks. Why did it stop?
You won't find a word in the decision of West Coast Hotel Co. v. Parrish, 300 U.S. 379 (1937), that repudiated the freedom of contract doctrine that had been used to invalidate New Deal legislation. But, this decision and others that followed (such as Wickard v. Filburn, 317 U.S. 111 (1942) in which the Supreme Court held that wheat grown for personal consumption on your own farm was interstate commerce) had a great deal to do with FDR's threat to expand the size of the Supreme Court and pack it with liberal justices (the "Court-packing plan"). When Roosevelt was re-elected in 1936, he proposed that one additional justice, up to ta total of fifteen, be appointed for each justice over seventy who did not resign or retire. He used neutral rhetoric about the limited abilities of older justices, but everyone knew that it was an end run arond the lifetime appointment clause.
It worked without ever being implimented. Indeed West Coast Hotel was, not coincidentally, decided while the Senate Judiciary Committee was debating the Court packing plan and the rejection of the plan that followed was attributed to this "switch in time that saved nine." But, even if the Court packing plan had been implimented, the plan was well within the constitutional perogatives of Congress.
The Constitution does not mandate a nine person Supreme Court (indeed, it has been increased in size before). This flows only from the same sort of constitutional tradition that protects the filibuster. And, if the Republicans break that trust, the Democrats should follow suit by packing the Supreme Court with liberal justices when they eventually return to power. Indeed, the very threat of a possible court packing later, may make Republicans leary of trying to rush extremists through by ignoring the filibuster now. The mere fact that federal judges are appointed for life, does not mean that the only way the balance of power can be changed in the Supreme Court is to let the conservative justices die off.