Sen. Ron Johnson, R-Wis., charged Thursday that Medicaid expansion under Obamacare is fueling the opioid crisis in America, and said he has evidence to support his theory.

Johnson sent a letter Thursday to the Health and Human Services inspector general that said he used open-source databases and "shockingly identified 261 people who had been convicted – in states ranging from Pennsylvania to Vermont – of exploiting Medicaid cards to obtain opioids, which were often resold at enormous profit."

The letter included an examination of overdose deaths in geographically similar states from 2013 to 2015. For example, the letter cited Centers for Disease Control statistics and Census data when claiming that during those years, the state of Maine, which didn't expand Medicaid, saw a 55 percent increase in overdose deaths, while the nearby expansion state of New Hampshire saw a 108 percent increase in overdose deaths.

Johnson's letter did not draw a perfect causal link between the two by suggesting Medicaid is the prime driver of the opioid crisis. But it offered up enough case studies to suggest that the expansion since 2014 has contributed.

Johnson told the HHS inspector general that internal data from the agency showed that overdose deaths, "largely from opioids, are surging much faster in Medicaid expansion states than in non-expansion states."

"The number of convictions for improperly using Medicaid to obtain opioids, identified through such a cursory search, suggests a larger systemic problem," Johnson concluded. "Because opioids are so available and inexpensive through Medicaid, it appears that the program has created a perverse incentive for people to use opioids, sell them for large profits, and stay hooked."

Numerous recent reports in the media have suggested that changes or rollbacks to Medicaid expansion would be harmful in the ongoing battle against opioid addiction.

For example, National Public Radio interviewed Lynn Cooper, the director of the Drug and Alcohol Division at Pennsylvania's Rehabilitation and Community Providers Association, who said the expansion is helping to fight the crisis.

"[T]he problem we had before Medicaid expansion is that many people were not eligible despite the fact that they were very poor and unemployed," Cooper said in describing Pennsylvania's drug addiction treatment efforts. "Before Medicaid expansion, our counties were running out of money. Now, today, this Medicaid expansion has absolutely stopped that. And a lot of the people that the county funds were paying for are now being covered by Medicaid expansion."

Another article by The Atlantic argued that funding opioid treatment through block grants is less effective than people having comprehensive health coverage.

At the same time, commentary from the right side of the political spectrum has made the same points Johnson made in his letter.

"While Medicaid may in some cases provide additional treatment options for an addict who is willing to engage, it also provides a 'free' plastic card loaded with unlimited government funds that often increases access to opioids," wrote Sam Adolphsen in the conservative National Review earlier this month.

Medicaid expansion and how to manage it has played an important role in the debate over healthcare reform this year as Republicans have struggled to "repeal and replace" Obamacare.

The opioid crisis was also an important topic of the 2016 presidential campaign for both Hillary Clinton and Donald Trump, and since being inaugurated, President Trump has created an opioid task force with New Jersey Governor Chris Christie as the chair.