Mr. Trump has praised the goals of the Obama-era program, called Deferred Action for Childhood Arrivals, or DACA, but has said that it’s unconstitutional. That argument has been rejected by lower courts, which have ruled that the decision to shut it down was “arbitrary and capricious.”

Background: DACA shields young immigrants from deportation and allows them to work. The status lasts for two years and is renewable, but it doesn’t offer a path to citizenship.

Go deeper: The 2017 memo announcing the end of DACA relied on a strictly legal argument, rather than one based on policy objections. That memo is now at the heart of what experts say is a major weakness in the government’s case.

“The Daily”: Today’s episode is about the case.

President Trump, Ukraine and impeachment

For months, Mr. Trump focused on one of the weakest countries in Europe as a potential solution to his political problems. A 30-minute phone call in July with Ukraine’s leader has since emerged as a major threat to Mr. Trump’s presidency.