The Justice Department revealed Monday that it will side with a federal district court ruling last year that found the Affordable Care Act, or Obamacare, unconstitutional.

The decision is a significant reversal from the agency's previous stance, which declared that certain aspects of the law, like the "individual mandate," are unconstitutional, but could be severed from the law's main framework.

The decision means that the government will not defend the law's constitutionality on appeal.

What is the background?

Last December, District Court Judge Reed O'Connor ruled Obamacare unconstitutional after the Republican-led Congress passed tax reform legislation in late 2017 that removed the tax penalty for not having health insurance.

The Supreme Court infamously upheld Obamacare's individual mandate in 2012 under the declaration that it was a "tax." But because the tax reform law gutted the individual mandate, O'Connor ruled that "the remainder of the ACA is non-severable from the individual mandate, meaning that the Act must be invalidated in whole."

O'Connor's ruling was almost immediately appealed to the 5th Circuit of Appeals, which has yet to issue a ruling. Obamacare has remained in place while the appeals process remains ongoing.

What did the DOJ say?

In a letter to the clerk of the 5th Circuit Court of Appeals, Assistant Attorney General Joseph Hunt and Deputy Assistant Attorney General Brett Shumate wrote that "the Department of Justice has determined that the district court's judgement should be affirmed."

During his Senate confirmation, now-Attorney General William Barr admitted he was open to reconsidering the government's position on Obamacare. Monday's announcement is likely a result of fresh examination by senior-level DOJ officials.