The United States refugee program, long a pillar of American foreign policy, has experienced dramatic ups and downs in recent years.

During his first term, President-elect Donald J. Trump drastically reduced the annual refugee cap. In 2020, the final full year of that term, the United States admitted about 11,000 refugees, a record low.

Then President Joe Biden revived the program. In the fiscal year that ended Sept. 30, about 100,000 refugees arrived to the country, the largest tally in nearly three decades.

Now, with Mr. Trump vowing to crack down on immigration again, refugee resettlement agencies are bracing to be gutted. They are scrambling to secure funding to keep alive operations that support refugees already in the country, and are trying to expedite the arrivals of people waiting in camps in Kenya, Jordan and Uganda.

“It makes my heart clench when I see a family scheduled to arrive after Jan. 20,” said Cynthia Shabb, executive director of Global Friends Coalition, a nonprofit in Grand Forks, N.D., that receives refugees from around the world.

“If Trump shuts resettlement down, no one will come,” said Ms. Shabb, as she scanned a list of people from Afghanistan, Somalia and Central America who are expected to arrive in the coming months.