Something like two thirds of the US federal budget is spent on some form of welfare. Assuming you want to keep that ratio you could spend more per person with fewer people withdrawing from that system.
The US doesn’t lack the capital for welfare. The country decides to instead waste its resources fighting wars, fighting its allies, fighting its trade partners. The money is here, there is no will to allocate it to welfare. You could reduce the number of people on welfare by a massive amount and none of the savings from that would get distributed to the remaining recipient
On average, foreign born US residents use less public assistance then native born.
Completely wrong, except possibly if you're defining Social Security as welfare, in which case honesty would compel you to note that no one draws Social Security except based on having previously made contributions via dedicated taxation for social security.