Isn't it kind of shortsighted to look at helping people abroad as not helping domestically?
If they get help in their country or homeland - which they must care about (the US doesn't have a monopoly on patriotism) - maybe they won't want to reluctantly look elsewhere for a better life.
Fewer people will want to go to America for "a better life" or believe going to the US is the only way they can support their family back home.
The US's burden of humanitarian relief is shared with private citizens. There will be fewer refugees, economic migrants. You won't have to want to build a wall.
People abroad might have money to buy US products. If Americans are seen as a good force, there will be fewer terrorists who want to fight it.
The US and private US citizens doing things abroad helps the US domestically.
It's like when people were angry about Ford creating jobs in Mexico. That's as many Mexicans who won't need to "steal" jobs in the United States! Wanting Mexicans to not have jobs will create more Mexicans who want to get into the US to get jobs.
But back to your actual comment...
They do have a United States Division that funds education programs and health care programs domestically.