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Damian Dovarganes, Associated Press
Californians join health care workers at a rally to save the Affordable Care Act across the country outside LAC+USC Medical Center in Los Angeles, Sunday, Jan. 15, 2017. The rally was one of many being staged across the country in advance of President-elect Donald Trump's inauguration on Jan. 20. Trump has promised to repeal and replace the health care law, and the Republican-controlled Senate on Thursday passed a measure taking the first steps to dismantle it.

WARREN, Mich. — Thousands of people showed up in freezing temperatures on Sunday in Michigan to hear Sen. Bernie Sanders denounce Republican efforts to repeal President Barack Obama's health care law, one of dozens of rallies Democrats staged across the country to highlight opposition.

Labor unions were a strong presence at the demonstration in a parking lot at Macomb Community College in the Detroit suburb of Warren, where some people carried signs saying "Save our Health Care."

Lisa Bible, 55, of Bancroft, Michigan, said she has an autoimmune disease and high cholesterol. She said the existing law has been an answer to her and her husband's prayers, but she worries that if it's repealed her family may get stuck with her medical bills.

"I'm going to get really sick and my life will be at risk," said Bible, an online antique dealer.

President-elect Donald Trump has vowed to overturn and replace the Affordable Care Act, and majority Republicans in Congress this week began the process of repealing it using a budget maneuver that requires a bare majority in the Senate.

"This is the wealthiest country in the history of the world. It is time we got our national priorities right," Sanders told the Michigan rally.

The law has delivered health coverage to about 20 million people but is saddled with problems such as rapidly rising premiums and large co-payments.

Britt Waligorski, 31, a health care administrator for a dental practice, said she didn't get health insurance through work but has been covered through the health law for three years. While the premiums have gone up, she said she is concerned that services for women will be taken away if it is repealed.

"It's done a lot for women for their annual checkups, for mammograms -- women's health in general. If this gets repealed, we're going to go back to the old days when that's not covered," she said.

At the rally in San Francisco, Silvia Pena, a 45-year-old nanny, said she had never had held insurance until she enrolled in the Affordable Care Act six years ago.

"I don't have health issues, but you can need insurance any time. We should all have access to health services," said Pena who held a sign that read "It's our right and our body. Keep Planned Parenthood and Obamacare."

The health law has provided subsidies and Medicaid coverage for millions who don't get insurance at work. It has required insurers to cover certain services such as family planning and people who are already ill, and has placed limits on the amount that the sick and elderly can be billed for health care.

Sanders, a strong supporter of the law, made several visits to the state last year during the Michigan primary and defeated Hillary Clinton there. But in a major surprise, Michigan narrowly voted for Trump on Nov. 8, the first Republican presidential candidate to carry the state since 1988.

Rallies in some other cities in support of the health law also were well attended. Police estimated about 600 people showed up in Portland, Maine. Hundreds also attended events in Newark, New Jersey, Johnston, Rhode Island, Richmond, Virginia and Boston.

Republicans want to end the fines that enforce the requirement that many individuals buy coverage and that larger companies provide it to workers.

But they face internal disagreements on how to pay for any replacement and how to protect consumers and insurers during a long phase-in of an alternative.

This version of the story corrects Lisa Bible's age and the name of the community college in Michigan.

AP reporters Patrick Whittle in Portland, Maine, Bruce Shipkowski in Trenton, New Jersey, Sarah Rankin in Richmond, Virginia, Collin Binkley in Boston and Olga R. Rodriguez in San Francisco contributed to this story.