Political scientists draw an elementary distinction between two models of representative democracy, both first articulated by British political philosopher Edmund Burke. In the first, termed the “delegate model,” elected officials exist only to articulate the voice of their constituents. Like the monstrous king that adorned the original cover of Hobbes’ “Leviathan,” these public officials are theoretically mere agglomerations of the people they represent, possessing no opinion or will separate from the collective voice of the voters.

In the second, termed the “trustee model,” voters elect the best candidate to office in the hopes that he will wisely exercise his own judgment in the service of the public interest, regardless of how his constituents may feel about each particular issue. Voters entrust power to such a trustee, Burke thought, in order that “his unbiased opinion, his mature judgment, his enlightened conscience” may benefit the public at large, especially when dealing with particularly complex issues about which the masses may be uninformed. “Your representative,” remarked Burke, “owes you, not his industry only, but his judgment; and he betrays, instead of serving you, if he sacrifices it to your opinion.”

American democracy has generally sought to strike a balance between these two models, with each historical era favoring one or the other to a degree conditioned by the needs and prevailing temperament of the people. The Framers – distrustful of a trustee-like “virtual representation” model in the British Parliament under which each Member theoretically represented the whole Empire but in reality cared little about the welfare of the American colonists – deliberately favored the delegate model, embedding in our Constitution an electoral system whereby each member of Congress directly represented the interests of the State from which they hailed. As concerns about “pork barrel” spending and distaste for narrow partisan interests have grown, however, the trustee model has swung back into vogue. No longer is it intellectually fashionable for senators or representatives to openly admit to hoarding federal dollars in their state or district, for example, although the delegate model would (and does) encourage such tactics.

Both models have their advantages. American democracy benefits most when our representatives are both directly beholden to the wishes of the people and free to exercise their own expert judgment on specific issues about which voters know little or have no clear opinion.

But recent events have made clear the greatest danger of a delegate model run amok: the dumbing-down of democracy to the commonest denominator.

When interviewed by GQ for its December issue, for instance, Florida GOP Senator Marco Rubio refused to give a clear answer to the simplest of questions: “How old do you think the Earth is?”

“I’m not a scientist, man,” replied Rubio carefully. “I’m not sure we’ll ever be able to answer that. It’s one of the great mysteries.”

Let’s be clear here. Mr. Rubio is an intelligent, educated man, and well aware that the Earth is billions of years old. But in order to get elected by a crowd of conservative Florida Republicans almost as old as they think the Earth is — in other words, the constituents he’s supposed to represent — he’s got to pretend like he doesn’t have a clue.

Under the limits of a pure delegate model, representatives are required to act as stupid as their constituents really are. That perverse constraint on our national intelligence is the primary subject of Pennsylvania Governor Ed Rendell’s biting memoir, “A Nation of Wusses: How America’s Leaders Lost the Guts to Make Us Great.” A discouraging chronicle of “politicians pretending to stand on principle while, in fact, pandering to their bases” and “flip-flopping on issues, not because of new information, but because of new polls,” “A Nation of Wusses” exposes an American political class increasingly willing to abandon brains and bravery for political gain, whether on the age of the Earth or global warming. It’s a sad story of people who know better deliberately trying not to.

In some sense, a pure delegate model is the American Dream materialized — a Washington populated entirely by Mr. Smiths, average guys and gals just like us.

But such a model also requires that those average guys and gals limit themselves to averageness. To strive for anything more or better would be to become a trustee, to use one’s own wisdom and experience to serve the public good to the fullest, and to grow beyond the confines of the mold imposed by the unexceptional median voter. Such a model leaves no room, in short, for Lincolns — politicians who eschew the safe, easy choices in favor of what they know to be right and true.

The question is, do we want our representatives to serve us best, or to actually be us? I’ll take the former.

Shoot Miles your best guess as to the age of the Earth at milesu1@stanford.edu.