The U.S. Senate is a very peculiar institution. It was not when it started. It was created to be a check on the popularly elected House of Representatives, but also on the President, through its "advise and consent" power--the President's nominees for officials had to be confirmed by the Senate. Senators were not to be elected, but to be appointed by the state legislatures. The assumption was that the legislatures would want to appoint a person of distinction to represent the state. There were only 13 states (though more were envisioned), so there would be only (at the outset) 26 Senators. Their long terms (six years) would encourage expertise and a greater independence from popular passions than the members of the House of Representatives, elected for only two-year terms, could be expected to have. The Senate would, in short, be an elite, deliberative, and only indirectly democratic body.
The change in the character of the Senate since the Constitution of 1787 has been profound. Senators, as a result of a constitutional amendment, are now directly elected, and there are 100 of them. The combination of the amount of time that they have to spend raising money and tending to constituents, and the immensely greater populations of most states now compared to the eighteenth century, and the enormously greater size and complexity of the federal government, have resulted in Senators' being underspecialized, despite having large staffs. The filibuster (a creature of Senate rule rather than of the Constitution or a statute) creates a requirement of a supermajority to pass legislation to which there is substantial senatorial opposition, and rules or customs of senatorial "courtesy" give individual Senators considerable blocking power, for example power to delay confirmation hearings.
The result is that the Senate is an extremely inefficient institution compared to the House of Representatives, in which the majority is in firm command. And because there are so many more House members (435), they have fewer committee assignments and thus can develop greater expertise than Senators; in addition, although they run for office three times as often, they run in much smaller districts and often with little competition and on both accounts don't have to raise as much money in campaign donations as Senators do.
Since the Senate is very large and Senators are directly elected, it is unclear why there is a Senate--that is, why the federal legislature is bicameral. Bicameralism increases the transaction costs of enacting legislation, which can be good or bad (it is bad in national emergencies, as in the financial crisis of last September), and it also increases the cost of repeal, which on balance probably is bad, arbitrarily enhances the political power of sparsely populated states, results in many unprincipled and confusing legislative compromises, and diffuses responsibility for legislation. It is not clear that on balance we are better off with the bicameral system.
The filibuster is an incomprehensible device of government. A supermajority rule, whether it is the rule of unanimity in criminal jury trials or the supermajority rules for amending the Constitution, makes sense when the cost of a false positive (convicting an innocent person, or making an unsound amendment to the Constitution) substantially exceeds the cost of a false negative. But it is hard to see the applicability of that principle to Senate voting, given the other barriers to enacting legislation.
These reflections on the filibuster are prompted by the Democratic Party's recent achievement of a filibuster-proof (60-40) majority in the Senate. It might seem that since the President Obama and Vice-President Biden made such a strenuous effort to convert Senator Arlen Spector from the Republican to the Democratic Party, which put the latter within one vote of a filibuster-proof majority, they must think that having such a majority is a political asset. I am not so sure they do think that. It is easy to see why the conversion was in the Democratic Party's interest regardless of its potential effect on the filibuster; by eliminating one of the Republican Party's most prominent moderates, it contributed to the growing marginality of that party, as it becomes increasingly identified with a rather shrunken right wing.
I am not sure the filibuster-proof majority is a boon to the Democratic Party and program. Because if now the Administration's legislative program fails of passage or is mutilated in the course of passage, it will not be possible to blame an obstructive minority consiting of filibustering Republican windbags. Furthermore, the new voting alignment increases the power of every Democratic Senator, by threatening to align himself with the 40 Republicans in a crucial legislative showdown, to thwart the Administration's program or, more realistically, to insist on what may be costly compensation in the form of an amendment favoring an interest group that is important to his electoral prospects. Indeed, each of the Democratic Senators now has an incentive to play the hold-out in order to extract concessions, in any situation in which Republicans need only one or a very few Democratic defectors in order to defeat an Administration bill.