"You gotta pay your bills!". Trump has been clear about what is required for the USA to protect Europe.
In 2016, when he first took office, only four NATO countries reached the two-percent target for defense spending (excluding the USA). This year, 23 of 30 European allies are expected to reach the target. Sweden and Finland are two of them.
But Trump is unlikely to be satisfied, believes Charly Salonius-Pasternak, a researcher at the Finnish Institute of International Affairs in Helsinki.
I don't think for a second that he will say "it's going in the right direction" and "I understand that you have national budget problems". That's not Trump, he says.
On the contrary, Trump may insist that NATO's spending target is raised further, to 2.5 or even 3 percent.
He can say, "very nice – but the new level is 2.5 if you want to be protected".
Has a point
And Salonius-Pasternak believes that Trump has a point. He highlights that the first time Americans pointed out that Europe must do more was already in the late 1960s.
The very idea I think is completely right. We shouldn't even do it because we're afraid of Trump, but for our own security.
Some NATO countries should certainly spend 4–5 percent for a period because they literally don't have enough ammunition, tents, or military healthcare.
The question is whether the NATO allies in Europe are ready to dramatically increase their military spending. Maybe they have no choice; Trump has warned that he would encourage Russia to do "whatever they want" with NATO countries that don't contribute enough.
It has been interpreted as him being willing to break with NATO's Article 5, which states that all members are obliged to help a country under attack. But Trump's team has noted that the language in Article 5 is "flexible" and does not require a member to respond with military force, according to an article in Politico last summer.
Bring home troops
That Trump would formally leave NATO seems unlikely to Charly Salonius-Pasternak.
Instead, he can withdraw American personnel from NATO commands, pay less to NATO's joint budget – and bring home parts of the 100,000 American soldiers stationed in Europe.
But I would be surprised if he did it immediately. He is very much into other countries respecting the USA, partly due to military strength. There are probably some Republicans who would argue that it doesn't look strong to withdraw from all this.
But the USA may also want to focus more on China, and Salonius-Pasternak warns European leaders not to become complacent.
They can't lean back with the thought that "we don't need to do anything".
NATO wants member countries to allocate 2 percent of GDP to defense.
Expected defense spending as a percentage of GDP in 2024
Poland: 4.12 percent
Estonia: 3.43
USA: 3.38
Latvia: 3.15
Greece: 3.08
Lithuania: 2.84
Finland: 2.41
Denmark: 2.37
United Kingdom: 2.33
Romania: 2.25
North Macedonia: 2.22
Norway: 2.20
Bulgaria: 2.18
Sweden: 2.14
Germany: 2.12
Hungary: 2.11
Czech Republic: 2.10
Turkey: 2.09
France: 2.06
Netherlands: 2.05
Albania: 2.03
Montenegro: 2.02
Slovakia: 2.00
Croatia: 1.81
Portugal: 1.55
Italy: 1.49
Canada: 1.37
Belgium: 1.30
Luxembourg: 1.29
Slovenia: 1.29
Spain: 1.28
Source: NATO