President of the EU Council Donald Tusk has fired a warning at US President Donald Trump telling him to “appreciate your allies, after all you don’t have that many.” But perhaps he needs to take a look at the numbers.

The condescending swipe at the Commander-in-Chief of the world’s largest military power came just before President Trump arrives in Brussels for the NATO Summit, which is to be held tomorrow.

Donald Tusk went on to warn Mr Trump that he would be isolated on the world stage and suggested he should think twice before criticising the EU.

However, perhaps Mr Tusk should actually have a think around President Trump’s rhetoric and whether there is logic behind it, rather than throwing public shade towards the most powerful leader in the world.

The concerns Trump is voicing are not new. The past three US presidents, who have represented both political sides, have all made clear they believe the relationship has been imbalanced for too long. The Wales summit in 2014 should have settled the issue; this is where it was agreed by all leaders in NATO that there must be an agreed spend of 2 per cent of GDP on defence.

Yet, here we stand four years later and just three Member States from the EU spend 2 per cent of GDP on Defence; Estonia, Greece and the UK.

The number too, was not picked out at random. It is a reflection of the real challenges NATO countries face. Europeans and Americans created the alliance nearly 70 years ago, and together we have kept a bond to protect democracy, prosperity and free and open societies. If the EU is genuinely serious about defence spending, as President Tusk seems to think they are, then it is time to put his money where his mouth is.

NATO is a highly successful military alliance. But its success depends on vigilance and on cooperation. The threats we face today are more varied, complex and changing than we saw in the Cold War. They range from terrorism to cyberattacks, from North Korean saber-rattling to Russian revanchism. They represent a new and demanding set of security challenges, and NATO has to be able to respond.

Of course meeting these challenges doesn’t just mean increasing cash. NATO using the KPI of the three “Cs”- cash, capabilities and commitments. But cash is undoubtedly the most important of these three elements.

Donald Tusk and Donald Trump at the NATO Summit in 2017.

Looking at the numbers, one can easily understand the frustrations of the US Government. NATO has 29 members and the US accounts for 72 per cent of its total budget. That is not a figure President Tusk can hide behind and no wonder successive US Presidents have expressed frustration at their European Counterparts.

Too many European governments have been complacent about the ongoing security threats. Even after the Russian annexation of Crimea in 2014, some continued to make cuts to their military budgets.

President Tusk needs to actually pay attention to what is being said to him and not who is saying it. Whatever his thoughts are on the US President, Trump is actually talking sense and his thoughts on this matter are not new. What we are seeing though, is President Tusk making a pointed statement because he thinks he can play games with his US Counterpart.

However, Security is too important to play games with. European countries need to not only fulfil their promises on defence spending, but to demonstrate that they understand the merits of that spending. They must show that they can pay their way. NATO is built on the concept of mutual understanding. Europe must show it can play its part in this essential alliance.