President Donald Trump has again assailed fellow NATO members for not contributing enough to the alliance while maintaining a trade surplus with the US, keeping up a drumbeat of criticism before meeting European leaders this week in Brussels.
On the eve of his departure for the two-day NATO summit on Wednesday and Thursday, Trump linked two well-worn gripes: funding for the North Atlantic Treaty Organisation and other countries' trade practices.
"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," Trump wrote on Twitter on Monday.
In another tweet, the Republican president complained about Europe's trade surplus with the US. Trump has slapped tariffs on billions of dollars worth of steel and aluminium imports from China, the European Union, Canada and others, prompting retaliation against US products. He is considering extending the levies to the car sector.
Trump has been a harsh critic of NATO since the 2016 presidential campaign. After taking office, he affirmed the US commitment to the defence of NATO allies but kept up complaints about Washington shouldering the financial burden.
By current standards, Washington funds about 70 per cent of NATO spending. NATO members have agreed to spend 2 per cent of economic output on defence every year by 2024, but Germany and Spain are among the countries not expected to meet the target.
At the first NATO summit he attended last year, Trump denounced Europe's low defence spending and called for NATO to be on the front line against Islamic militants. He also surprised many NATO leaders by urging them to focus on illegal immigration.
This year, trade is on his mind.
"I'm going to tell NATO: You've got to start paying your bills. The United States is not going to take care of everything," Trump said at a rally last week. "They kill us on trade."
Founded to deter the Soviet threat in 1949, NATO is based on deep co-operation with the US, which provides for Europe's security with its nuclear and conventional arsenals.
NATO has found renewed purpose since Russia's 2014 annexation of Crimea, sending battalions to the Baltics and Poland to deter potential Russian incursions.
