Today, Donald Trump is in town and his presence in London today for North Atlantic Treaty Organisation meetings is causing jitters in the Conservative camp, as the Tories worry about the U.S. president's unpredictability and tendency to say things without necessarily thinking through the consequences.
Fellow NATO leaders will be relieved that Trump, who derailed last year's summit agenda with his demands, appears to be satisfied with how the allies have stepped up their military investment.
He said his trip would be focused on "fighting for the American people".
The US leader is due to hold a number of bilateral meetings alongside the main summit over two days, and will dine with Queen Elizabeth at Buckingham Palace on Tuesday.
"We are faced with a paradox", Stoltenberg told Reuters.
Europe, Turkey and Canada will pledge $400 billion in defence spending by 2024, aiming to placate President Donald Trump who has long said US allies need to spend more on the collective defence.
The meeting is expected to consider new threats, including in the areas of cyber and space, after the alliance last month declared space one of its operational domains alongside air, land, sea and cyber.
His frustration at a USA troop withdrawal in Syria in October that set the stage for Turkey's unilateral offensive into northern Syria prompted Macron to describe the alliance as "experiencing brain death", as he decried a lack of strategy. And Stoltenberg reports that a majority of NATO's 29 members now plan to hit the 2 percent threshold by 2024. He has also defied his allies to buy Russian anti-aircraft missiles despite a threat of US sanctions.
Wariness of Russian Federation may prove to be a unifying factor, diplomats said.
At past meetings, he has berated European leaders for failing to contribute more financially to the costs of collective defence.