President Trump repeatedly expressed his disappointment during the weekend that Republicans failed to pass a healthcare bill that would repeal and replace portions of Obamacare. To increase pressure for a bill to pass, he questioned why members of Congress don't pay the same for healthcare as other people who have Obamacare plans.

"If ObamaCare is hurting people, & it is, why shouldn't it hurt the insurance companies & why should Congress not be paying what public pays?" he asked on Twitter.

The question centers on a provision in Obamacare that went into effect in 2014, one that lawmakers understood at the time would be politically sensitive. Members of Congress and their staff aren't specifically exempt from Obamacare and their plans changed as a result of the law, but they also don't receive the same coverage as, for instance, someone who is self-employed.

Prior to Obamacare, members of Congress received healthcare coverage under the Federal Employees Health Benefits Program, the same program that covers 8 million people who work for U.S. government agencies or who are retired from the federal government. This meant that their employer, the federal government, contributed funding to their healthcare plans.

When Obamacare passed, Sen. Chuck Grassley, R-Iowa, introduced an amendment that said Congress should be required to follow the same laws it imposed on everyone else, and so part of the law obligated Congress and its staff to buy Obamacare plans.

Most people who buy on the exchange, however, do not receive money from an employer to purchase coverage. The exchanges were intended to help people who could not get health insurance through a job or the government.

This meant that members of Congress and their staffs were facing significantly higher premiums. Lawmakers worried that low-paid staff, in particular, would seek work elsewhere when faced with such price increases.

In response, the Office of Personnel Management in 2013, under the Obama administration, issued a rule that said members of Congress and their staff could buy health insurance from the small business exchange in the District of Columbia, called "SHOP." The rule allowed them to keep government contributions, which pays for about three-quarters of their premiums.

Without the rule, lawmakers and their staff would have had to pay more under Obamacare than other federal employees. They also would have become the only workers in the U.S. who were blocked from getting help from an employer.

The rule led to charges from opponents that Congress had exempted itself from Obamacare. It also became part of a lawsuit filed by the conservative group Judicial Watch but was dismissed by a D.C. judge.

Trump isn't the only one to call for a change to the provision. Sen. Ron Johnson, R-Wis., had planned to file an amendment to strip the contributions if a GOP healthcare bill had gone forward.

After the bill failed, Jenny Beth Martin, co-founder and national coordinator for the Tea Party Patriots, said Friday that she thought the policy should be scrapped for members of Congress and their staffs as a way to motivate them to pass a healthcare bill.

"To unite congressional Republicans, President Donald Trump should take action to end the congressional exemption from Obamacare," she said. "It is apparent that since members of Congress, their families and staff do not have to live under the law they passed for every other American, they lack the incentive to take the action they were elected to take. Ending Congress's special exemption from Obamacare will motivate Republicans to finally keep their promise — if not for principle, at least to improve their own insurance predicament."

Unlike the laws that dictate coverage for most Americans who use the exchange, which require an act of Congress for significant overhaul, the small business rule can be changed through administrative action.