Why is Donald Trump putting Nato alliance in the firing line?

Donald Trump heads to Brussels on Wednesday for the Nato heads of Government summit amid fears over his commitment to the transatlantic alliance.

The military bloc set up to counter Russia in the Cold War has often been in his firing lines, starting when he was running for office in 2016 and then after he took office in 2017.

What is Trump's problem?

Money. He is unhappy at how much the other 28 members of Nato contribute. In March 2016 he said it was "obsolete and disproportionately too expensive" and on Monday, ahead of the summit, he suggested (on Twitter, of course), that "by some accounts, the US is paying for 90% of Nato" and on Tuesday raged: "NATO countries must pay MORE, the United States must pay LESS. Very Unfair!"

Is that correct?

Mr Trump has been accused of not really understanding the funding. Nato members, who along with the US and UK include Canada, Turkey and every major country in Western Europe, committed in 2006 - before the global economic crisis - to pay a minimum of 2% of their gross domestic product (GDP) on defence. But this is not the same as paying contributions into Nato's relatively small coffers directly.

How much do countries spend on defence then?

As you might expect of the world's only military superpower, the United States pays more than others. It spent 3.58% of GDP in 2017, according to figures from the House of Commons Library. In comparison the UK paid 2.14%, but just six of the 29 members spend more than the 2% figure. France (1.79%) and Germany (1.22%) are among those who do not.

What does Mr Trump want?

A defence spending splurge. He has called on other Nato states to increase their spending, at least to the 2% mark they agreed 12 years ago. On Monday he tweeted: "The United States is spending far more on NATO than any other Country. This is not fair, nor is it acceptable. While these countries have been increasing their contributions since I took office, they must do much more. Germany is at 1%, the U.S. is at 4%, and Nato benefits Europe far more than it does the US."

What does Nato say?

The funding area of its website states that the US accounts for two-thirds (67%) of defence spending of the alliance. It added: "The combined wealth of the non-US Allies, measured in GDP, exceeds that of the United States. However, non-US Allies together spend less than half of what the United States spends on defence. This imbalance has been a constant, with variations, throughout the history of the Alliance and more so since the tragic events of 11 September 2001, after which the United States significantly increased its defence spending."

Why does this matter now?

Vladimir Putin. The not-exactly glacial relationship between Russia's autocratic leader and the volatile American president has caused some angst in diplomatic circles. The two are due to meet in Helsinki on July 16 following Mr Trump's visit to the UK at the end of the week. Any moves to weaken Nato, which was formed in 1949 as a bulwark against Russia - then the USSR - would play right into Putin's hands.

What could Trump do?

He could withdraw US troops from Europe. There are currently around 65,000 American military personnel in Europe, down from several hundred thousand during the Cold War. A withdrawal would weaken European defences against any Russian aggression. Putin has already shown he is prepared to use military force on his neighbours, invading the Ukraine to annex Crimea in 2014. Former Soviet states, especially in the Baltic, fear they could be next.

What has been the reaction?

Countries including France and German have already agreed to up their defence spending. Others are waiting to see what Mr Trump has to say in Brussels in July 11.

European Council President Donald Tusk has insisted that the US has no better ally than the EU.

In a pointed apparent reference to Mr Trump's meeting with Mr Putin, Mr Tusk noted that European military spending "is an investment in our security, which cannot be said with confidence about Russian and Chinese spending".

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