Don Humbertson, a 64 year old lung cancer surviver, is examined by Dr. Wade Harvey at the Clay-Battelle Community Health Center March 21, 2017 in Blacksville, West Virginia.

The number of Americans without health insurance increased by about 3.2 million in the first year of Donald Trump's presidency, which featured a series of efforts to undercut the Obamacare law, a new survey finds.

A total of 12.2 percent of all adults now lack health insurance, an increase of 1.3 percentage points since the last quarter of 2016, according to the Gallup-Sharecare Well-Being Index.

The last quarter of 2017 saw no significant change in the uninsured rate, according to the survey.

But that spike in the uninsured rate over the course of 2017 is the biggest single-year increase measured since the survey started asking Americans about their health insurance status in 2008.

The rise in uninsured rates was most pronounced among younger adults, blacks, Hispanics and low-income people.

The increases reverse a consistent series of drops in the uninsured rate since the Affordable Care Act, as Obamacare is formally known, began taking full effect in January 2014.

That year was the first in which most Americans were required to have some form of health insurance or pay a tax penalty, and also the first in which coverage from individual health plans sold on Obamacare marketplaces was available.

In the third quarter of 2013 — the last quarter before Obamacare plans went on sale for 2014 coverage — the uninsured rate stood at 18 percent of adults.

The uninsured rate began plummeting thereafter, falling to 13.4 percent in the first quarter of 2014, and to 10.9 percent by the last quarter of 2016.

An estimated 20 million people gained health insurance coverage through the ACA, which included not only the offering of plans sold on the Obamacare exchange but also the expansion of Medicaid benefits to more poor adults in most states.

But that downward trend in the uninsured rate reversed as Trump took office in January 2017.

The new Trump administration promptly pulled back on enrollment promotion efforts in the last days of the Obamacare open-enrollment season last January. The administration also embarked on a series of efforts to repeal and replace much of the ACA through congressional action.

Those efforts failed last year.

But as Gallup noted in a write-up of its survey's latest findings, "media coverage of the policies to repeal and replace the healthcare law may have caused some consumers to question whether the government would enforce the penalty for not having insurance."

Trump has continued to publicly disparage the law, which in October he falsely claimed did not exist anymore. He also cut back significantly on the advertising to encourage sign-ups in health plans during the recently completed enrollment period.

Other likely causes of the 2017 rise in the uninsured rate, Gallup said, are that a number of health insurers stopped selling Obamacare individual plans through government marketplaces and that, as a result, prices increased for plans that remained on those exchanges.

"This may have caused some Americans, especially those who failed to qualify for federal subsidies, to forego insurance," Gallup's write-up said.

And Gallup noted that "it seems likely that the uninsured rate will rise further in the years ahead," given the effective repeal, starting in 2019, of Obamacare's requirement that most Americans have some form of health insurance or pay a fine.

The tax bill passed by Congress last month included that gutting of the Obamacare individual mandate. The Congressional Budget Office has estimated that 13 million more Americans would become uninsured in the next decade because of that repeal, although some analysts say the increase will be less dramatic than that.

Insurance premiums in the individual coverage market are projected to be 10 percent higher than they otherwise would have been as a result of the mandate's repeal. Those price increases are expected to lead some people to opt out of coverage.