British politicians and European military experts have warned that Donald Trump’s decision to withdraw 9,500 troops from Germany risks handing a strategic advantage to the Kremlin and undermining the postwar western military alliance. It would also affect the United States’s ability to operate in the Middle East and Africa – although there is scepticism as to whether the notoriously fickle president will be able to carry out the threat before November’s election. Briefed on Friday to US newspapers, the proposal to remove a quarter of the US troops in Germany is yet to be confirmed publicly, and Berlin said on Monday it had yet to be formally notified of the mooted withdrawal. But the decision swiftly provoked concern. Jens Stoltenberg, Nato’s secretary general, spoke to Trump on Monday afternoon by phone when he said they discussed “the importance of keeping Nato strong in an increasingly competitive world”. That came after the defence chief made some pointed observations to the Nato 2030 conference: “The challenges that we face over the next decade are greater than any of us can tackle alone. Neither Europe alone. Nor America alone. So we must resist the temptation of national solutions.” Tobias Ellwood, the Conservative chair of the defence select committee in the UK parliament, said he was not certain that Trump’s decision was final and that it would be challenged by the US military. He said: “Weakening Nato in the hope this will lead to increased German defence is a dangerous game which plays into Russia’s hands.” Trump’s decision comes after several years of complaining about Nato, without taking any specific action. In July 2018 he threatened “go it alone” if Nato members – and in particular Germany – did not raise their defence spending to 2% of GDP in order to reduce the cost incurred by the US from providing transatlantic defence against Russia. Others add that the real damage would be to the already battered diplomatic credibility of the White House. Tom Tugendhat, the Conservative chair of the foreign affairs committee, said Trump’s surprising decision would encourage European nations “to listen less to the US” while he remained in power. Bastian Giegerich, director of defence and military analysis at the International Institute for Strategic Studies (IISS), said that until now “US officials had argued Europeans should not listen to what Trump says and instead look at what he does.” The latest threat means “this had gone out of the window”, he said. The move has been widely interpreted as a personal rebuff to Angela Merkel following what was reportedly a frosty phone call between the two at the end of May, when the German chancellor torpedoed Trump’s hopes to hold a G7 summit in the US in June. Historically, the military alliance between the two countries has been close. US troops have been deployed in Germany since the end of the second world war, and although the numbers are sharply down from the 400,000 at the height of the cold war, their presence is partly designed to deter Russian aggression. Jamie Shea, professor of strategy and security at the University of Exeter, said troop numbers “were always an exercise in political psychology” but one that mattered given that, with troops stationed in all three Baltic states, Nato faces as many as 500,000 Russian troops in its western military district. Estimates from the IISS thinktank suggest that the US spent about $36bn (£28bn) on European defence in 2018, compared with total defence spending of European Nato allies of $239.1bn; a cost that countries like the UK, France and Germany would not be able to make up, particularly in the light of the Covid-19 crisis. Experts say the US cannot operate in the Middle East or Afghanistan without the vast Ramstein air base in western Germany, which acts as a logistics staging post, while Stuttgart is also the headquarters of the US Africa Command as well as its European operations. Shea, a former Nato spokesperson and senior official, said: “I see a lot of pain and not much gain, as you still have to pay the troops wherever they are based,” although he wanted to see full details of what the US was proposing, amid reports that some of the US troops could be moved to Poland. But Karin von Hippel, the director general of the Royal United Services Institute, cautioned western countries from overreacting to what she described as characteristic grandstanding from Trump: “I just don’t think it will be implemented in the next few months before a presidential election because Congress or the Pentagon will find ways to block it; but if he wins, then, yes, anything can happen.”