Mrs. Clinton vigorously defends the Affordable Care Act and its reliance on private insurance, but she would make important changes to protect people from co-payments and deductibles that have been rising faster than their wages. She would create a new tax credit of up to $5,000 to help families pay high out-of-pocket medical costs and would require insurers to cover three visits to the doctor each year before people start paying to meet their deductible.

Both Mrs. Clinton and Mr. Sanders have taken strong stands against the sometimes exorbitant prices for prescription drugs that manufacturers set with no reasonable justification. Both would authorize Medicare to negotiate with drug companies to drive down prices — a move now prohibited by law, at Republican insistence — and both would allow Americans to import cheaper drugs from other countries. Mrs. Clinton would cap a patient’s out-of-pocket drug spending at $250 a month.

The leading Republican candidates are unanimous in calling for repeal of the health care reform law — Donald Trump has called it a “catastrophe,” and Jeb Bush labeled it a “monstrosity.” Yet they are remarkably tongue-tied on how they would replace it.

In the Sept. 16 debate among 11 Republican candidates, the issue came up only obliquely. None of the Republican candidates have endorsed government negotiations with drug companies; they believe private negotiations and competition among drug companies are working just fine to curb drug costs.