With the battle over the Affordable Care Act continuing in the courts, Sen. Joe Manchin, D-W.Va., took to Twitter to argue that millions of Americans have benefited from the law.

Manchin wrote, “Let’s be clear: throwing out the #AffordableCareAct without a plan in place would be horrific for West Virginians and Americans with preexisting conditions, and the nearly 20 million Americans who have gained health insurance since the law passed in 2010.”

Have nearly 20 million Americans gained health insurance since the law’s passing? We took a closer look.

What does the data show?

The Kaiser Family Foundation, a non-rofit that focuses on health care policy, has published data through 2017 that sheds light on Manchin’s statement.

The foundation’s data shows that since 2010, the number of Americans with health insurance has increased by about 35 million, an even higher number than Manchin cited. However, while the law passed in 2010, it didn’t fully take effect until 2014, so the more accurate year to use as the baseline is 2013.

However, the data still supports Manchin’s claim. In fact, he undershot the actual number. Since 2013, about 26.6 million people have gained health insurance.

It’s worth noting that the Affordable Care Act, while a major factor in this increase, is not the only one.

As the Baby Boom generation ages, more and more Americans transition into guaranteed health care under Medicare — about 10,000 a day. Because of this, some previously uninsured people would suddenly be counted as being insured upon turning 65. For this, they have Medicare to thank, rather than the Affordable Care Act.

In addition, the continuing economic recovery played a role in expanding the pool of insured people, by increasing the number of Americans who were employed and who, as a result, were able to secure health insurance through their employment.

That said, there’s little question that the Affordable Care Act played a role.

Between 2008 and 2012 — an equivalent five-year period before the ACA took effect — just under 10 million people gained health insurance, a much smaller number than the 26 million between 2013 and 2017.

Our ruling

Manchin tweeted, “Nearly 20 million Americans … have gained health insurance since (the Affordable Care Act) passed in 2010.”

From 2013, the year before the law took effect, to 2017, the number of Americans with health insurance rose by 26.6 million, meaning that Manchin actually understated the gains. It’s worth noting, however, that gains in Medicare and from employer-sponsored health care account for a portion of that increase, so the increase can’t be credited entirely to the Affordable Care Act.

We rate this statement Mostly True.

This article was originally published by PolitiFact.