During a meeting with US governors on Monday, President Donald Trump said the reason for the slowdown on the repeal and replacement of the Affordable Care Act was in part because "nobody knew healthcare could be so complicated."

Sen. Bernie Sanders disagrees.

When asked by CNN's Anderson Cooper on Monday night about the "complicated" comment, Sanders immediately burst into laughter.

"Some of us who were sitting on the health and education committee, who went to meeting after meeting after meeting, who heard from dozens of people, who stayed up night after night trying to figure out this thing, yeah, we got a clue," Sanders said. "When you provide healthcare in a nation of 320 million people, yeah, it is very, very complicated."

Trump said in interviews before he took office that he wanted to repeal and replace the Affordable Care Act, the healthcare law better known as Obamacare, within weeks of his inauguration. At a press conference on January 11, however, Trump said the repeal-and-replace process would be "very complicated stuff."

Recently, the timeline for a replacement bill has stretched out. Republicans are facing issues within their own party, as different factions of lawmakers disagree on how best to overhaul the healthcare system.

"Maybe now, maybe the president and some of the Republicans understand you can't go beyond the rhetoric," Sanders said. "'We're going to repeal the Affordable Care Act, we're going to repeal Obamacare, and everything will be wonderful.' Well it's a little more complicated than that."

Sanders, the independent Vermont senator who ran as a Democrat in the 2016 presidential campaign and who caucuses with Democrats, has been fighting with the party against the repeal, pointing to the more than 20 million people who have gained insurance under provisions of the ACA.

"You mean to say that Democrats should work with Republicans to repeal this legislation?" Sanders said. "No, I don't think our job is to work with them to repeal the legislation — our job is to work with them to improve the legislation."

Watch the exchange below: