Both Bernie Sanders and Hillary Rodham Clinton are trying to make the rising cost of prescription drugs an issue in the presidential campaign.

Mr. Sanders introduced a bill in Congress this month, spelling out a host of policy changes to drive down drug costs. Mrs. Clinton tweeted on Monday that her plan would be released Tuesday, and her campaign has released some details.

Here’s why prescription drugs are bubbling up to the top of the Democratic health care agenda: Drug prices are bubbling up. Per capita drug spending increased by more than $100 last year, a big jump. At the same time, a growing share of Americans are being asked to foot the bill for their medicines, even if they’re insured. The Affordable Care Act, which has expanded insurance coverage, didn’t do much to counteract those trends.

Voters have clearly noticed the higher drug costs. This year, a survey from the Kaiser Family Foundation asked people to identify health issues that they thought should be top priorities for the president and Congress. The No. 1 issue was making drugs for serious diseases affordable. The No. 2 issue: lowering the cost of prescription drugs. A follow-up survey in August found that 24 percent of people said that they or a family member had declined to fill a prescription because of the cost.