And now the health service is going into winter — a particularly busy period for hospitals — while dealing with a pension crisis, bed shortages and the prospect of a major flu outbreak. Medical chiefs are concerned about how they will cope.

“I would say that in the last five to six years, I haven’t seen confidence levels this low heading into winter,” said Siva Anandaciva, a chief analyst at The King’s Fund, a health care charity.

Ms. Barcroft lives in the Coventry area, a pocket of working-class Labour strongholds in central England being targeted by Mr. Johnson, and she is one of many voters for whom the health service has become the dominant issue in the days leading up to the election. Some polls show that the health service is neck and neck with Brexit as the most important issue to potential voters.

For Labour, success on Election Day is dependent in large part on whether it can pull the focus from Brexit and make a case that Mr. Johnson would squander precious public services.

The party has pledged to outspend the Conservatives by pumping an additional 26 billion pounds, or about $34 billion, into the health service annually by 2024. Eager to hold onto its mantle as the party of the National Health Service, Labour has also vowed to undo shifts in recent decades toward privatization — a move that would entail a major reorganization of the health service.

A Labour supporter for most of her life, Ms. Barcroft is sympathetic to Mr. Johnson’s message that Britain needs to get Brexit done, despite her misgivings about voting for it in 2016. But since then, she has also dealt with the ravages of an overburdened health service working under the cloud of Brexit.