Except for one year, two-plus decades ago, Democrats have controlled both houses of the California Legislature for nearly a half-century.

Moreover, most members of the Senate are former members of the Assembly, so one might assume that the two houses are in synch and so duplicative that it might as well be a one-house Legislature.

There’s a cogent argument for a unicameral legislative branch, but the notion that the two houses are merely mirror images of one another – Tweedle Dee and Tweedle Dum, as it were – is erroneous.

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In fact, they – and their leaders of the moment – are often in conflict, not unlike the historic rivalries between the nation’s supposedly unified military branches for mission and money.

At any given point, one house is the more activist, setting the agenda and generating legislation – the Senate most recently – while the other is more reactive as it yearns for primacy.

The Legislature’s endemic dissonance has been on stark display in recent weeks, most evidently over an issue that also divides the state Democratic Party: single-payer health insurance.

With Republicans threatening to dismantle, or at least scale back, Obamacare in Washington, the party’s left-wing – the so-called Berniecrats – has been demanding that California provide universal health care, including coverage for several million undocumented immigrants.

With the California Nurses Association providing the political horsepower, the Senate passed a single-payer bill without a mechanism to cover its $400 billion a year cost. Whereupon, Assembly Speaker Anthony Rendon declared it dead (or at least stalled) on arrival, terming it “woefully inadequate.”

That angered Sen. Bernie Sanders, the CNA and other advocates, who immediately denounced Rendon as a corporate puppet, although he’s drawn support from other unions. CNA leader RoseAnn DeMoro‏ posted a picture of the California bear with a butcher knife in its back on Twitter, with the blade of the weapon inscribed “Rendon.”

Rendon’s action late Friday also was a rebuff to Senate President Pro Tem Kevin de Leon, who’s garnered lavish national media attention as a self-appointed leader of California’s “resistance” to President Donald Trump.

However, Rendon could hardly have done differently, given his own persona as a publicity-shy leader more interested in making policy than headlines.

Had the Assembly passed a bill without a financing system, it would have been accurately portrayed as empty symbolism.

Had it added the huge taxes that single-payer coverage requires, it would have exposed Rendon’s vulnerable members to the wrath of voters who would be paying those taxes – especially since the Legislature just voted to raise unpopular gas taxes – and thus could have eroded the Democrats’ very thin legislative “supermajorities.”

Gov. Jerry Brown also plainly didn’t want a single-payer bill on his desk, given his own hope to be remembered as a careful steward of the public’s money. So Rendon’s act was, both politically and fiscally, the right thing to do, even if it made him a pariah to his party’s left-wing.

Nor is health care the only point of cross-Capitol conflict this year. Another is what form, if any, the state’s “cap-and-trade” system of limiting greenhouse gas emissions will take. De Leon has a version that conflicts sharply with the Assembly’s and rectifying the two to write something that Brown can accept and get the required number of votes is no mean feat.

Whatever happens on these two issues, the rivalry will continue until and unless we emulate Nebraska and conclude that a unicameral Legislature would, indeed, make more sense.