The proportion of uninsured Americans reached 13.7% during the fourth quarter of 2018, the highest rate since 2014, it was reported on Wednesday.

That rate also increased from 10.9% in 2016, a surge that corresponds to roughly seven million people.

The level was at 18% in 2012, a new research poll from Gallup found. After the Affordable Care Act (ACA) — or Obamacare — implemented its individual health insurance mandate in 2014, the uninsured rate fell to the 2016 level.

Obamacare’s marketplace exchanges started on Oct. 1, 2013 and coverage for most plans Americans purchased at the end of that year began on Jan. 1, 2014. Many states also expanded Medicaid at the start of 2014. However, several Republican governors today have rejected proposals to expand Medicaid — medical care aimed at helping low-income Americans — in their respective states.

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According to Gallup, the substantial rise in the uninsured rate could be due to several reasons. First, insurance premiums have gone up in multiple states, especially for certain types of Obamacare plans. Second, public marketing for health insurance plans has dropped. Another factor at play is President Donald Trump‘s October 2017 decision to end cost-sharing reduction.

Online enrollments for Obamacare saw a late surge last month in the waning days of the 2018 Open Enrollment period, despite a federal judge striking down Barack Obama‘s signature healthcare law. Top Republicans like Sen. Mitch McConnell (R-Ky.), the Senate Majority Leader, have vowed to repeal the ACA despite many failed attempts by the party to do so.

Sen. Bernie Sanders (I-Vt.), a self-described Democratic socialist and proponent of Medicare-for-All, blasted Trump in a tweet on Wednesday.

“We must end the embarrassment of being the only major country not to guarantee health care for all,” wrote the former 2016 presidential candidate.