Incumbent Davis, a Taylorville Republican, defeated Londrigan last fall by 2,058 ballots. He won 50.4 percent of the vote, while she carried 49.6 percent.

In announcing her candidacy among supporters at state AFL-CIO headquarters in Springfield, Londrigan focused heavily on health care, a theme of last year's campaign. She spoke about her own family's experience in 2009 when her son Jack, then 12, was battling a rare illness in pediatric intensive care.

"I ran last year to protect all families like mine whose access to good care and insurance were the only thing standing between them and financial ruin or, God forbid, the loss of a loved one because of an illness or medical emergency," she said. "I’m running for Congress in 2020 because we have unfinished business."

A spokeswoman for Davis said voters rejected Londrigan in November because of "liberal policies" she supports.

"Democrats in the House are being pulled further and further to the left by their caucus and Londrigan and anyone else running for Congress are going to need to tell voters where they stand,” spokeswoman Ashley Phelps said in a statement. “Londrigan is already on the record supporting Medicaid for All, she was endorsed by co-writers of the Green New Deal, and been supported by multiple candidates running for president."

Londrigan last year fought back against Republican ads that characterized her as supporting a single-payer system, also known as Medicare for All. She has said repeatedly she supports a “public option” that could compete with private insurance companies. Phelps last year pointed to a February 2018 candidate survey in which Londrigan said, "There are good options, such as Medicare X and Medicaid-for-All, being discussed," while also calling for other solutions.

The 2018 race was among the most-watched in the country as both parties poured in funding and brought national attention to the district. Vice President Mike Pence visited Springfield to campaign for Davis, while U.S. Rep. John Lewis, a Georgia congressman and Civil Rights icon, came to Decatur to campaign for Londrigan.

Brian Gaines, a political science professor at the University of Illinois at Urbana-Champaign, said it's not extraordinarily unusual for someone to announce his or her candidacy so far ahead of an election.

"It's not crazy to try and get your name out earlier," he said. 

The 13th District takes in parts of the Metro East outside of St. Louis and heads northeast to include Springfield, Decatur and the Champaign-Urbana and Bloomington-Normal areas.