The first president to propose a healthcare overhaul was Harry Truman. When an issue is around that long, ideas for tackling it proliferate, and a lot of groups form to push those ideas. If the fight over healthcare has gotten to seem a little bewildering, this is a big part of why: People are desperate for a change to the status quo. Yet the healthcare system swats away presidents and outlives Congresses. A joke around Washington is that healthcare reform is similar to a cicada swarm. Like the locusts, every 17 years it emerges from dormancy, makes a bunch of noise and then dries up into a husk.

The unpleasant but clear truth is that our jury-rigged healthcare system, liked by few consumers, still isn't hurting for defenders. There are, obviously, the insurance companies that have built their fortunes on the present system, and the actual healthcare providers who benefit well enough too. But even something as innocuous as cracking down on waste, fraud and abuse is politically dangerous, because someone in the industry always stands to gain from a patient's wasted dollar. The trick, which reformers still haven't quite figured out, is how to craft a plan that forces the beneficiaries of the status quo to behave, but doesn't provoke them into fire-breathing attack mode.

With Senate hearings starting up again Monday, Salon has put together a guide to the various approaches, and who's pushing them.

Single-payer: Liberals have spent generations aching for a government-run healthcare system. It seems to work for Canada, so why not for us? People like Medicare well enough, after all, and Medicare is single-payer, just not for everybody. Rep. John Conyers has drafted a bill, going exactly nowhere, to institute a plan much like the Medicare for All plan featured in the campaign platform of Rep. Dennis Kucinich.

The fact is that despite the backing of groups like Physicians for a National Health Program, single-payer is not happening. Sen. Max Baucus, a major healthcare player as Finance Committee chairman, declared, "Everything is on the table with the single exception of single-payer." Barack Obama, an explicit advocate of single-payer as a younger politician, got at the problem during the presidential campaign, saying, "If I were designing a system from scratch, I would probably go ahead with a single-payer system."

He is, of course, not designing a system from scratch. Shaping his effort to pass healthcare reform has been Obama's political need to be able to tell voters, as he often does, "If you like your plan and you like your doctor, you won't have to do a thing." Regardless of the general merits of single-payer, the president would be denied this argument if he were pushing Medicare for All. With an issue as complicated as healthcare, it's generally thought that the public can't possibly understand the policy details. So regardless of what kind of system people might actually want if they only understood -- hard enough to discern anyway -- GOP shrieking about the president's desire for "socialized medicine" would actually be true, and possibly even convincing, if single-payer were on the table. And that, Obama and virtually every key mover in Washington seem to agree, would be fatal for reform.

The public option: In order to capture some of the benefits of single-payer while dodging the political costs, liberal would-be reformers have mainly settled on what's known as "the public option" idea. At its strongest, this would work as a kind of opt-in Medicare for All. It could pay at Medicare's rates and, like Medicare, deliver much more care for the dollar. Usually, this idea is coupled with a mandate that everyone have insurance of some kind (and subsidies for people at a certain level of poverty), so the government could offer insurance directly to people who don't like their plan, or don't have a plan at all, without incurring the wrath of voters happy with their insurance. One prominent scholar warns, though, that a public plan might become a dumping ground for the sick, while the private insurers skim the cream off the system by only having to insure the healthy.

A public option also has the benefit of forcing private insurers to compete with Medicare-level rates. This would either improve private care significantly, the logic goes, or possibly kill it outright if it can't compete for insurance-buyers, easing the country into single-payer gradually and of its own will.

That's why insurance companies are putting aside their differences to try to throttle this thing before it gets off the ground. Or at least soften it acceptably. A number of compromise-minded pundits and politicians have suggested that a public option is only tolerable if it can't use Medicare's heft to keep prices low, or rely on government subsidies to break even. A weak public plan like this would be mostly toothless -- basically, a kinder, friendlier insurance company -- and hence much less threatening to private insurance.

The trigger plan: Some have proposed kicking the can down the road on a public plan, by writing the law without it, but including the threat that private insurers will "trigger" a public plan into being if they fail to quit their lowdown ways. If insurance companies were, for example, underserving or overcharging a particular region, the government might then offer that region a public plan. Note that a similar possibility for triggering a public plan was built into the 2003 Medicare Part D bill. Congress never pulled the trigger.

The co-op plan: Senate Budget Committee Chairman Kent Conrad, a North Dakota Democrat, has floated this compromise idea. Says Conrad, "In a 60-vote environment, you've got to attract some Republicans as well as holding virtually all the Democrats together, and that, I don't believe, is possible with a pure public option. I don't think the votes are there."

Conrad's co-ops would be seeded with federal money, and would follow the model, roughly, of credit unions. Owned by their members and functioning as nonprofits, they would allow people to pool their purchasing power to negotiate for cheaper care. Critics say co-ops would take years or even decades to get off the ground, and question if they would really lower costs significantly at all. A working health co-op called Group Health in Washington state, for example, has premiums similar to those of for-profit insurers, though it has been less ruthless about purging sick members.

The Republican plan: The GOP has had a hard time coming around to the notion that our healthcare system -- the envy of the world, remember -- needs systemic reform of any kind. When the Republican leadership's healthcare working group did finally produce its plan, it mainly touched on old classics: medical malpractice reform, unspecified tax reforms, and cracking down on waste, fraud and abuse. Suffice it to say that, as the Republicans have no chance of passing a plan, they didn't bother too much with the specifics.

There are plenty of details to be worked out besides the presence, and shape, of an alternative to private insurance. What will it all cost, and how will we pay? Will there be a mandate to buy insurance, for individuals and for employers? How much will the government subsidize people who are too poor to buy insurance? What kind of new regulations will govern the private insurers?

All of these are relevant to the ultimate outcome, and the House of Representatives, the Senate Finance Committee, and the Senate Health, Education, Labor and Pensions Committee may all produce different takes on these questions. But it's the public option that has become the heart of the fight, because it's the public option that would most fundamentally reshape the market through which Americans get healthcare.