A page on Sanders' website listed 41 different rallies today around the country.
Thousands braved frigid temperatures in Michigan to turn out for the rally there, The Associated Press reported. The event took place outside in the parking lot of Macomb County Community College and was live-streamed on Sanders' Facebook account.
“This is the wealthiest country in the history of the world,” Sanders said at the rally, firing up the crowd despite the cold. “It’s time we got our priorities right.”
The crowd responded to the speech with chants of "Bern-ie, Bern-ie!"
Among those attending was Lisa Bible, 45, of Bancroft, Michigan, who said Obamacare has been an answer to her and her husband's prayers.
"I'm going to get really sick, and my life will be at risk," Bible told the AP.
Democrats' aggressive display of support for the Affordable Care Act, including in smaller states like Hawaii and Delaware, is an attempt to pressure Republicans into backing away from dismantling the legislation.
On ABC News' "This Week,", Sanders warned Republicans against repealing Obamacare without anything to take its place.
"The vast majority of the American people agree with me and many others," he said. "You don't simply repeal the Affordable Care Act without a replacement."
Sanders' also left the door open to working across the aisle to improve the health care law.
“Nobody thinks that Obamacare is perfect. It has its problems,” he said, but, “Sensible people have got to work together.”