Protecting reproductive rights is one of Democrats’ strongest issues, and their ability to capitalize on it may decide a tight election. Chances are even better now with Kamala Harris, a candidate known for her unapologetic positions on the issue, at the top of the ticket.

And yet Democrats have not fully capitalized on this apparent advantage. Though Donald Trump was responsible for appointing the Supreme Court justices who were crucial in striking down Roe v. Wade — a campaign promise that thrilled parts of the electorate and dismayed others — in this election cycle he seems to have avoided the ire of many voters because he insists a second term won’t matter much to reproductive rights one way or another, especially in states that protect abortion access.

The reality is that a second Trump term — or a first Harris term — could fundamentally change Americans’ reproductive lives and health. With Ms. Harris formally introducing herself to voters as the Democratic presidential nominee next week at the party’s convention, now is the time to make the case for what she could do — and what Mr. Trump might — over the next four years.

It will not be enough to blame Mr. Trump for abortion bans already on the books or to warn that he wants to pass a nationwide ban. Ms. Harris, like President Biden, has vowed to sign into law a bill “restoring and protecting reproductive freedom in every state.”

These messages are powerful, but they look to the past or point to possible futures that voters may dismiss as unrealistic — and thus inapplicable to their lives. Ms. Harris needs to drive home that in a post-Roe world, Mr. Trump would probably have unusual power to criminalize abortion. She must also convey that under a Republican administration, there would be no state in the country where reproductive rights would be absolutely secure. Furthermore, she has a chance to overcome a problem that plagued Mr. Biden’s campaign: explaining what could be done to expand reproductive rights.

Ms. Harris, who has worked to connect Mr. Trump to Project 2025, the plan created by conservative groups and former Trump officials as a blueprint for the next Republican president, must remind voters that many key conservative proposals for reproductive rights in a second Trump administration would not require congressional approval. Mr. Trump, she must emphasize, could do a great deal of damage through the use of executive power alone.