The week after Democrats spent much of their national convention attacking him over his position on abortion rights and reproductive health, former President Donald J. Trump said on Thursday that he would require insurance companies or the federal government to pay for all costs associated with in vitro fertilization treatments if he is elected in November.

Mr. Trump’s announcement — made in an NBC interview, a speech in Michigan and a town hall in Wisconsin — came with little detail about his proposal or how he might address its cost. For one cycle, the treatments can cost up to $20,000 or more. But he has been trying to rebrand himself to voters on reproductive access and abortion rights, issues that have cost Republicans at the ballot box.

Mr. Trump, who often on the campaign trail has bragged about his role in appointing Supreme Court justices who voted to overturn Roe v. Wade, last week on social media declared that his administration “will be great for women and their reproductive rights,” a phrase used by abortion-rights advocates.

The post appeared to be an effort by Mr. Trump to cast himself as more of a political moderate on abortion, an issue that could hurt him in November.

On Thursday, Vice President Kamala Harris’s campaign accused Mr. Trump of trying to run from his record on abortion access.

“Trump lies as much if not more than he breathes, but voters aren’t stupid,” Sarafina Chitika, a spokeswoman for the Harris campaign, said in a statement. “Because Trump overturned Roe v. Wade, I.V.F. is already under attack and women’s freedoms have been ripped away in states across the country.”