In her new book “What Happened” — officially out on September 12 — Hillary Clinton wrote that her biggest regret from the the campaign trail was saying that she would put coal miners out of business.

CNN, which obtained a copy of the book this week, reported that the 2016 Democratic presidential nominee said that comment was the one “I regret the most.”

Clinton made the remark during a town hall in Columbus, Ohio in March 2016, during which she touted her plan to replace fossil fuel-based energy production with renewable systems.

“I’m the only candidate which has a policy about how to bring economic opportunity using clean renewable energy as the key into coal country,” she said. “Because we’re going to put a lot of coal miners and coal companies out of business.”

She quickly added that she wanted to help coal miners and other workers who gave their health and sometimes their lives to produce the nation’s energy.

“And we’re going to make it clear that we don’t want to forget those people,” she added. “Those people labored in those mines for generations, losing their health, often losing their lives to turn on our lights and power our factories.”

Clinton later called the comment a “misstatement” that she mistakenly made “out of context.”

But the remark sparked a backlash against Clinton and haunted her throughout the campaign, which Republican presidential candidate Donald Trump worked to center around the suffering of white working class Americans, with a particular focus on struggling coal miners.

She later lost every county in West Virginia — the country’s premier coal mining state — to her Democratic opponent Bernie Sanders in the primary — a dramatic reversal from her landslide win against Barack Obama in the state’s 2008 Democratic primary.

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