Duopoly Unchecked, Imbalanced

Perhaps one of the more insidious mystifications of duopoly ideology is the confusion of the two-party system with the constitutional separation of powers. I have remarked on this obfuscation before. Two recent quotes of note expose the extent to which duopolist politicians are in on the act too. Denying that he would switch his party affiliation in March, Arlen Specter stated that his remaining a Republican was best for the two party system, as mentioned yesterday. However, the full quote reads:

The United States very desperately needs a two-party system. That's the basis of politics in America. I'm afraid we are becoming a one-party system, with Republicans becoming just a regional party with so little representation of the northeast or in the middle atlantic. I think as a governmental matter, it is very important to have a check and balance. That's a very important principle in the operation of our government. In the constitution on separation of powers. (Emphasis added.)

In markedly similar terms, the Queen's County Republican Party has endorsed media mogul Michael Bloomberg's candidacy for a third term as mayor or New York City (via Urban Elephants):

The Mayor's stated belief in a strong vital two party system being a necessary check and balance in government, and Bloomberg's past support for the Republican State Senate conference and commitment to GOP Party building on a local level also were cited as major reasons to back the Mayor. (Emphasis added.)

This is all the more ironic given the fact that Bloomberg has been a Democrat, a Republican, and is now apparently an independent and has sought the endorsements of the Independence and Working Families Party, in addition to those of Republicans in NY's fusion ballot system. Nontheless, those who refer to the duopoly as if it were a system of checks and balances seem to mean that, in the two-party system, the ideal state is a state of relative equilibrium, within which each party works to 'check' and 'balance' the other. It is thus an argument against lop-sided majorities. In addition, it works as an argument for a specific division of labor between the parties in government - that is, for divided government -, which, significantly, presumes that the constitutional separation of powers is essentially non-functional when the same party controls both the legislature and the executive. There is certainly some truth to this position. An activist rubber-stamp congress coupled with a militant unitary presidency is a dangerous thing. Divided government could perhaps be considered an extra-constitutional guard "against those encroachments which lead to a tyrannical concentration of all the powers of government in the same hands," as Madison put it in the Federalist No. 48. But it is hardly a "check and balance," and it is certainly incapable of restricting the concentration of power in the context of the reigning bipoligarchy. In point of fact, it has become just another form for such concentration.

In the first half of the twentieth century, divided government was something of an anomaly, breaking up periods of undivided government by one party or the other, while in the second half it became a kind of norm, occasionally interrupted by periods of undivided party rule. (If the Wikipedia chart is to be trusted, that is.)

Is the apparently widespread sense that the two party system is a part of the system of constitutional checks and balances likely a relatively recent phenomenon then? Or does it have a much longer history?