That would be hardly none, because that's not how NATO works.
Trump has long claimed that various NATO members have failed to pay their “bills,” “dues” or “NATO fees,” that they “owe us a tremendous amount of money” or that they “owe NATO billions of dollars.”
Facts First: All of these Trump claims are false. While a majority of NATO members do not meet the alliance’s target of each member spending a minimum of 2% of gross domestic product on defense, the 2% target is a “guideline” that does not create bills, debts or legal obligations if it is not met. In fact, the guideline doesn’t require payments to NATO or the US at all. Rather, it simply requires each country to spend on their own defense programs.
When Trump was president, the guideline was written in forgiving language that made clear that it was not a firm commitment. That version of the guideline, created at a NATO summit in Wales in 2014, said members that had yet to reach 2% would “aim to move towards the 2% guideline within a decade with a view to meeting their NATO Capability Targets and filling NATO’s capability shortfalls.” In other words, the members that were below 2% in 2014 didn’t even have to promise to hit the target by 2024 – simply to make an effort to do so by then.
NATO does require members to make direct contributions to fund the organization’s own operations. But there is no sign that members have failed to make those contributions, which constitute a tiny fraction of the allies’ defense spending, and Trump has made clear that his talk of debts is about the 2% guideline.