Setback on Immigration Policy Goal Leaves Trump Fuming Over Makeup of Courts

“They may be foolish enough to go after DACA again, but I hope they know and see that America has the DREAMERS’ backs,” Cecilia Muñoz, who served as Mr. Obama’s top adviser on Hispanic issues and domestic policy, wrote on Twitter. She added a warning to the president and his aides about the political power of the pro-immigrant movement.

“We see you, Donald Trump, we see you Stephen Miller,” she said, “and we’re coming for you.”

Whatever the president decides to do, the debate over what happens to the Dreamers in the long run will play out most starkly in the presidential contest between Mr. Trump and the presumptive Democratic nominee, former Vice President Joseph R. Biden Jr.

Mr. Biden hailed the ruling on Thursday and vowed to introduce legislation on his first day in office that would give the young immigrants permanent legal status in the United States. Efforts to pass such legislation have failed for more than a decade, but he said the court’s temporary protections raise the stakes of the November election.

“I will continue to stand with DACA recipients, their parents and their families at every step, and in November, joined by millions across this country, we will reject the president who tried to rip so many of our family members, friends and co-workers out of our lives,” Mr. Biden said in a statement.

The issue is already at the forefront of several key Senate races. Hours after the ruling, a Democratic group issued a news release seeking to make an issue out of what they claimed was opposition to DACA by by Senator Cory Gardner, a moderate Republican from Colorado.

The group cited two votes to undermine the program that Mr. Gardner took in 2014 and 2015 as a member of the House. “No amount of election season revisionist history from Gardner can change that,” wrote Zach Hudson, a spokesman for the group, American Bridge.

But since becoming a senator, Mr. Gardner has backed bipartisan efforts to find a legislative solution to give Dreamers a permanent legal status, including a path to citizenship. In a statement on Thursday, Mr. Gardner said he advocated such measures: “I support immediate passage of the Dream Act and would also support the House-passed Dream and Promise Act. The Senate should act quickly to provide permanent relief for Dreamers.”