By Morgan Haefner

The number of working-age Americans without health insurance grew by an estimated 4 million since March 2017, according to the Commonwealth Fund's ACA Tracking Survey.

The U.S. uninsured rate among working-age Americans now rests around 15.5 percent, compared to 12.7 percent about a year ago. Lower-income families earning less than $61,000 saw the biggest jumps in uninsured rates when compared to 2016 numbers, according to the Commonwealth Fund.

The Commonwealth Fund attributed the increase to two factors: a lack of legislative fixes to the ACA's weaknesses and changes to the law initiated by President Donald Trump's administration. These include cutting ACA advertising and the open enrollment period for ACA marketplace coverage.

That being said, 11.8 million Americans enrolled in health plans on the ACA marketplace during the 2018 open enrollment period, only down about 1 million from 2016, prior to the Trump administration's changes.

Still, "signs point to further erosion of insurance coverage in 2019: the repeal of the individual mandate penalty included in the 2017 tax law, recent actions to increase the availability of insurance policies that don't comply with ACA minimum benefit standards, and support for Medicaid work requirements," according to the report.