For years, former President Donald J. Trump has tried to stir up fears about immigrants with claims of caravans full of criminals and rapists heading toward America’s southern border.

In Tuesday night’s debate with Vice President Kamala Harris, he doubled down on the vitriol, promoting a debunked conspiracy theory that Haitian immigrants were killing Americans’ house pets and eating them for dinner.

Mr. Trump’s political goals appear to be the same as they always have been: to stoke anger and give people someone to blame for their misfortunes.

But the debate highlighted how Mr. Trump has escalated his assaults on immigrants in the 2024 presidential campaign, and how he uses the issue to overshadow other topics, including tariffs or the economy. Mr. Trump’s first mention of “dangerous” migrants on Tuesday night came just 59 seconds into his first answer — one about the future of the economy.

For her part, the vice president appeared unwilling to get into a back-and-forth on the issue, despite the fact that illegal border crossings have dropped dramatically following tough measures ordered by President Biden. An executive order he signed in June curbed people’s right to seek asylum, among other restrictions.

In July, the number of arrests at the southern border stood at just over 56,000, the lowest since the record figures in December, when around 250,000 migrants crossed.