Like a chink in a dam, Gov. Peter Shumlin’s concessions to the business community on participation in a new health benefits exchange threaten to open a chasm that could blow the dam wide open.

Shumlin announced last week that he was broadening the category of businesses that would not be required to purchase insurance from the exchange that state officials are now constructing to serve as a marketplace for health care policies. Creation of the exchange follows the requirements of the federal health care reform law and is meant to create a steppingstone to a new single-payer system for Vermont.

Shumlin decided that businesses with between 50 and 100 employees could opt out of buying insurance through the exchange. He also decided the state would allow so-called bronze plans to be sold. These are low-cost, high-deductible policies that are the only affordable option for some businesses.

These concessions by Shumlin alarmed health care reform advocates who feared that by allowing more people to obtain coverage outside the exchange, the governor was undermining one of the essential purposes of the new system.

The idea behind the health care exchange and the single-payer system that is meant to replace it is to put together a risk pool large enough so that health care expenses may be spread broadly and the cost for participants will be constrained. A risk pool of 100 could be bankrupted by one highly costly case. A risk pool of 500,000 could share the cost more easily.

But some business people are leery of the mandate that they must choose from the limited range of policies offered on the new exchange. To blunt criticism, Shumlin extended the exemption to a wider range of businesses. One of Shumlin’s point men on health care reform, Steve Kimbell, said the concession to business would not hurt the administration’s reform effort. Side-stepping opposition at the early stage was meant to guarantee success later — “because the biggest path to failure is to be too ambitious too soon,” he said.

Until now, Shumlin has pursued a different method — taking on health care reform with a plan so ambitious that it could potentially sweep away all opposition. Thinking big was thought to be the only way to achieve such a big goal. Now supporters of reform worry that the plan will be nickeled and dimed to death.

Late last week business leaders in the state decided to pile on, perhaps sensing that Shumlin had shown weakness and that now was the time to find an escape hatch from his health care plan. “Our goal is to have a voluntary exchange and to have the products inside of it be of such excellent quality and price that businesses will flock to the exchange,” said Betsy Bishop, executive director of the Vermont Chamber of Commerce.

There is irony in the effort to lasso Vermont businesses into an exchange where they would find the policies for their employees. That’s because if Shumlin’s program goes according to plan, business would eventually be able to get out of the business of health insurance altogether. One of the aims of the single-payer system as envisioned by Shumlin is to separate health care from employment. Businesses would no longer have to pay for health insurance at all. Vermonters would obtain coverage from state-offered plans that were not connected to their jobs.

In the meantime, Shumlin is trying to transform the present employment-based system into an employment-based system that uses the exchange as a mechanism in common. But without broad participation, the exchange could follow the path of Catamount Health, which became too expensive to maintain. If that were to happen and if the exchange were to fail, Shumlin’s single-payer hopes could be dashed on the shoals of concession and compromise. It is a difficult challenge — to compromise where necessary and useful without selling out your basic principles and abandoning your fundamental goals.