The Trump administration has announced that it is cutting aid to Pakistan, days after the president threatened on Twitter to do so.
He's also made similar threats towards the Palestinians, as well as towards countries that backed a United Nations resolution opposing the recognition of Jerusalem as Israel's capital.
So what are the ways in which a US administration can cut off foreign aid?
The answer is complicated, and depends on the type of aid, as well as the specific country or group receiving it.
So it would be almost impossible for the president to cut off aid from all 128 countries that voted for the UN resolution in one fell swoop.
Holding the purse strings
It is the US Congress, not the president, that has the final say on the foreign aid budget.
Because all spending has to be signed off by Congress, it "holds the power of the purse strings", says Erin Collinson from the Center for Global Development, a non-partisan think tank based in Washington and London.
Congress can approve or alter the administration's budgetary proposals and can also specify in substantial detail where it wants the aid to go - even if that's in opposition to what the president wants.
However, in situations where Congress has not gone into specifics, an administration has a considerable amount of flexibility about how exactly it spends the allocated budget - although it has to notify Congress of its intentions.
In the case of cutting aid to the Palestinians, US officials told the Associated Press that one option for Mr Trump would be to reroute aid which would normally go directly to the Palestinian Authorities to other NGOs working directly with the US Agency for International Development.
It's not only Pakistan that we pay billions of dollars to for nothing, but also many other countries, and others. As an example, we pay the Palestinians HUNDRED OF MILLIONS OF DOLLARS a year and get no appreciation or respect. They don’t even want to negotiate a long overdue...— Donald J. Trump (@realDonaldTrump) January 2, 2018
...peace treaty with Israel. We have taken Jerusalem, the toughest part of the negotiation, off the table, but Israel, for that, would have had to pay more. But with the Palestinians no longer willing to talk peace, why should we make any of these massive future payments to them?— Donald J. Trump (@realDonaldTrump) January 2, 2018
In some cases, Congress will attach conditions to foreign aid, which could allow the president to stop it without having to run it by Congress.
For example, in the case of Pakistan, most aid is conditional on the US secretary of state certifying that certain conditions - mostly related to counter-terrorism cooperation - are being met.
This gives the administration the power to hold back the aid, by refusing to do that.
In fact, the Trump administration has already held back foreign aid to Pakistan under these conditions. In September it withheld $255m (£188m) in military aid to the country, precisely by claiming it was not meeting its counter-terrorism obligations.
What aid to Pakistan is being suspended?
The $255m is approximately a third of total US aid to Pakistan - other aid covers funds for education, energy, food and health.
Although the US ambassador to the UN said recently that President Trump was willing to stop all funding, the State Department said that civilian assistance programmes were not included in the suspension.
The US also sends millions of dollars through the Coalition Support Fund (CSF) - this is military assistance that reimburses Pakistan for counter-terrorism operations, and is not counted as US foreign aid.
Reuters quoted the Pentagon as saying up to $900m in CSF had been authorised for the 2017 fiscal year, and that this was being frozen.
State Department officials said they could not yet put a dollar value on how much aid was being cut in total, and told reporters that "the suspension is not a permanent cut-off at this time".
What if there's a stalemate?
Often any disagreements between the administration and Congress are worked out informally, says Curt Tarnoff of the US Congressional Research Service.
If they aren't - for example, if the president refuses to spend the money specifically requested by Congress - a process called impoundment could be triggered.
The matter could end up being decided in the Supreme Court.