Trump's budget plan includes cutting foreign aid, which is currently about one percent of all federal spending, or one dollar out of each one hundred spent. Cutting foreign aid to zero wouldn't do much to reduce the federal deficit, but it could weaken the powers of US foreign diplomacy to avert unrest in this world.
Catherine Rampell in the Washington Post speculates that a focus on cutting foreign aid comes about because not even the Republicans are that keen to cut domestic programs, to give more money to the military. She also describes a recent poll which shows that many people are uninformed of the tiny size of foreign aid in the overall federal spending:
Rampell notes: "In fact, of all the programs included in this survey, “foreign aid” garnered the highest share of responses calling it a major contributor to federal debt."
This is fascinating. A 2015 survey also noted that people vastly overestimate how much is spent on foreign aid:
A large majority of the public overestimates the amount of the federal budget that is spent on foreign aid. Similar to past Kaiser polls, just 1 in 20 correctly state that 1 percent or less of the federal budget is spent on foreign aid. About half say it is more than 10 percent of the budget, and, on average, Americans say that spending on foreign aid makes up roughly a quarter of the federal budget.
Bolds are mine.
I wasn't able to find the size estimates by political affiliation, but more Republicans than Democrats believe that foreign aid contributes to the national debt, and 63% of Trump voters in the recent survey believe that foreign aid greatly contributes to the federal debt, while only 34% of Clinton voters agreed with them.
All this makes me wonder about the confidence of beliefs which are not based on factual data. This article is worth reading in that context.