On Wednesday, President Obama joined Senate Democrats at their retreat, urging them to "finish the job" on health-care reform "even though it's hard."

That crowd knows how hard it can be. To get the 60 votes needed to pass the health-care bill last Christmas Eve, Senate Majority Leader Harry Reid worked furiously. The final holdout was Ben Nelson, a centrist Democrat from Nebraska. With time running out, Reid offered to have the federal government pay for the expansion of the state's Medicaid program in perpetuity -- and Nelson signed on to the bill.

Members of both parties were vociferous in criticizing the "Cornhusker kickback," as it came to be known. "That's not change we can believe in!" crowed Lindsey Graham (R-S.C.). "That is the worst in politics."

He's right about one thing: That wasn't change. It was a type of deal as old as the Senate itself. Back in the summer of 1787, the founders debated how to structure the legislature. James Madison, of the large state of Virginia, drafted a plan for a bicameral parliament, with both chambers apportioned by population. William Paterson, of the smaller state of New Jersey, called for a single house. In July, they compromised: two houses, one proportionate to population and one with two representatives per state.

The Great Compromise was intended to make sure the big states didn't trample the little guys. But today, with 37 more states on the scene, the little ones wield disproportionate power. "Half of the population of the nation lives in 10 states, which have 20 senators. The other half lives in 40 states that have 80 senators," says the official Senate historian, Donald Ritchie. Small states and states whose representatives might tip the balance on a key vote make out like bandits, as their senators demand outsize appropriations in return for their support. The Nelson fracas was nothing other than the Senate working exactly as it was designed to.

But what if the 100-member Senate were designed to mirror the overall U.S. population -- and were based on statistics rather than state lines?

Imagine a chamber in which senators were elected by different income brackets -- with two senators representing the poorest 2 percent of the electorate, two senators representing the richest 2 percent and so on.

Based on Census Bureau data, five senators would represent Americans earning between $100,000 and $1 million individually per year, with a single senator working on behalf of the millionaires (technically, it would be two-tenths of a senator). Eight senators would represent Americans with no income. Sixteen would represent Americans who make less than $10,000 a year, an amount well below the federal poverty line for families. The bulk of the senators would work on behalf of the middle class, with 34 representing Americans making $30,000 to $80,000 per year.

Imagine trying to convince someone -- Michael Bloomberg, perhaps? -- to be the lonely senator representing the richest percentile. And what if the senators were apportioned according to jobs figures? This year, the unemployed would have gained two seats. Think of the deals that would be made to attract that bloc!

Or how about if senators represented particular demographic groups, based on gender and race? White women would elect the biggest group of senators -- 37 of them, though only 38 women have ever served in the Senate, with 17 currently in office. White men would have 36 seats. Black women, Hispanic women and Hispanic men would have six each; black men five; and Asian women and men two each. Women voters would control a steady and permanent majority -- making, say, discriminatory health-care measures such as the Stupak Amendment and the horrible dearth of child-care options for working mothers seem untenable.

What about a Senate in which voters cast ballots for candidates campaigning to win over a certain age group? Thirteen senators would vie for 18-to-24-year-olds, who strongly support measures such as the cap-and-trade climate bill and marriage rights for gays. Nearly all of these senators would be Democrats. Americans over 65 would control 16 seats -- and would be mostly Republicans interested in protecting Medicare and the broader status quo. The baby boomer bubble would be largely in the eldest category, though its stragglers would round out the segment of voters, probably split between the parties, that is edging up on retirement. Thirty-six senators would serve 25-to-44-year-olds, and 35 senators 45-to-64-year-olds -- and would be likely to push the very issues now on the table, including health care, entitlement viability and tax breaks for the middle class.

However you slice it (or us), a new voting model would shake up the Senate's agenda. A senator vying for the $60,000 bracket -- filled with working parents concerned with putting children through school -- might need to promise Pell Grant reform and improved school lunches. One can imagine a coalition of senators for the elderly and senators for 20-somethings working to loosen federal laws around medical marijuana.

These deals, of course, would be very different from the deal Ben Nelson cut for Nebraska. But they highlight a truth so obvious it isn't often examined: Senators represent states. And states' priorities can seem strange when viewed in a national light. The Great Compromise promised just the kind of last-minute deal that Nelson struck, ensuring that the needs of his small state were recognized in the nationwide initiative.

These days, people don't much like the anti-democratic structure of the Senate and the bring-home-the-bacon politics it begets. Recent polls have shown that Americans despise the upper chamber -- more than the House, more than the White House. But you can't blame Nelson for doing exactly what the founders asked him to do.

annie.lowrey@foreignpolicy.com

Annie Lowrey is an assistant editor at Foreign Policy magazine.