WASHINGTON - The US Supreme Court on Wednesday ended three days of oral argument in a landmark case involving the Affordable Care Act, the signature healthcare overhaul of President Barack Obama.

During the session, the justices weighed the "severability" of a mandate that forces people to buy health insurance or pay a fine.

Arguments of "severability" followed Tuesday's debate on whether the mandate, which is at the core of the reform, is constitutional. Deputy Solicitor General Edwin Kneedler said if the court throws out the mandate, it would have to strike two other provisions along with it: the requirement that insurers cover anyone who applies and the ban on charging higher prices to customers with preexisting conditions, the most popular elements of the law. The government argued that the rest of the law could stand, even after striking the individual mandate.

The court also heard arguments Wednesday over the healthcare law's Medicaid expansion. States that filed the challenge claimed the expansion amounts to "coercion" because no state could afford to give up so much federal money. The federal government will initially pay for the entire Medicaid expansion, then cut its share to 90 percent.

After three days of argument, US media are predicting the court is poised to rule the mandate unconstitutional, although a verdict is not expected before June.

The White House, however, said Wednesday it remains "confident" that the health care reform law is constitutional and is implementing all the provisions of the law.

In a daily briefing, principal deputy press secretary Josh Earnest said they have "no contingency plan in place" if the law is thrown out, and he said the administration is "focused on maximizing the benefits of this law."