Today at 3pm ET, the Senate will begin debate on their health care bill. Over the next month, hours of speeches will be made, dozens of amendments will be offered, all kinds of votes will be taken. Vice President Biden kicked off the debate with a video showing doctors and nurses arguing for reform.

Ultimately, the bill’s fate will be determined by deals made off the floor of the Senate, not on it, however. Here are the top storylines going into the debate:

Cost. Somehow, we got back onto a debate about the cost of the bills, and particularly their impact on the federal budget deficit, which is what turned everyone’s blood cold in the spring and summer months of the debate. The fact that the bill is fully paid for while expanding coverage to 30 million or more Americans isn’t enough – it has to also significantly reduce deficits to satisfy the bean-counters. It actually does so – $130 billion by 2019, $650 billion in the following decade, but fiscal scolds don’t see this as credible and think Congress will weasel out on the changes and not realize enough savings.

Regarding the cost that individuals actually care about, the cost of their premiums, MIT’s Jonathan Gruber released a new report that shows individual and small group premiums going down under the Senate bill relative to the status quo. Gruber’s report shows major savings at the low end of the income scale, and modest savings at the high end. Ultimately, that’s what will matter to people. The White House was quick to tout the report.

Immediate Reforms. The biggest near-term problem with both bills is that they do not provide enough tangible benefits immediately, and people will quickly wonder why they should be pleased with a “reform” not phased in for years. David Hilzenrath writes about this today, noting that the major Senate reforms don’t hit until 2014. And even with those reforms, there is not the substantial police force to monitor the insurance industry to ensure compliance.

Until 2014, insurance companies could continue to deny coverage or charge higher premiums based on people’s medical history. Another highly touted reform — banning annual and lifetime limits on coverage — would take effect in 2010, but it would permit significant exceptions.

Even with those rules in place, “there’s no power to really hold the insurance companies accountable,” said consumer advocate Betty Ahrens, executive director of the Iowa Citizen Action Network. “It’s toothless.” [...]

At issue is the practice known as rescission, in which insurers revoke policies after policyholders become severely ill or injured. To avoid paying big medical bills, insurers search policyholders’ original applications for grounds to cancel the policies, such as failure to disclose preexisting conditions.

A 1996 federal law called HIPAA, the Health Insurance Portability and Accountability Act, prohibited rescissions unless consumers defrauded the insurer or deliberately misrepresented their medical condition. But the federal agency responsible “has done nothing to enforce those rights or to ensure that states do so,” Rep. Henry A. Waxman (D-Calif.) said in a hearing last year.

The lack of a federal regulatory apparatus for the insurance industry, as well as the failure in the Senate bill to repeal the industry’s anti-trust exemption and unleash the Justice Department, will make it extremely difficult for the regulations to actually take hold. A proper risk adjustment mechanism in the exchanges, essentially paying insurers to take higher-risk patients, would also help stop insurers from gaming the system, but the risk adjustment currently in place is insufficient.

The Public Option. A newfound push to minimize the public option has taken shape. One New York Times article asserts that the public does not care one way or the other about it. Another, from health care expert Paul Starr, says that the current version on offer is so de-fanged that it should be dropped in exchange for real measures to improve the bill.

This again assumes that health care is a static policy that will never change once this bill passes into law. Building upon a weaker public option which has the structure in place is far, far easier than putting it into creation all over again. And keeping the public option is undoubtedly easier than any of the reforms Starr wants to add, which would cost hundreds of billions of dollars. The New York Times editorial board seems to have this figured out.

Even with the constraints, a public plan could be a useful part of health care reform. Most important, it would compete in markets dominated by one or two private insurers that can charge more and not worry about losing customers.

The presence of a public plan could serve as a brake on unwarranted premium increases by the private companies. The C.B.O. said a public plan with negotiated rates would place “downward pressure on the premiums of private plans.” A public plan would also provide a safe harbor for people who do not trust the insurance industry and would prefer a government plan even if its premiums were higher. And it would be a place to test innovative ideas for controlling costs and improving quality.

Obviously, getting these points past the roadblock of four Democratic Senators – Mary Landrieu, Joe Lieberman, Ben Nelson and Blanche Lincoln – will not be simple. Who knows what they’ll concoct.