Honestly, it depends upon how much longer he remains president.
Obviously, the longer he is president the more damage he can and will do.
He already has harmed the USA in ways that no other president has,
at home and abroad and much more severely.
It's part of the reason he was officially graded as the worst US president in history.
The time for the recovery of the US reputation in the eyes of it's allies would partly
depend upon who the next presidents were and also how much effort they put into
restoring faith with our allies. But, damage has certainly been done and trust has been broken.
The following is an interesting article from earlier today;
In response to: US reputation will take ‘years to recover’ from Trump presidency, warn experts
John Haltiwanger
The Independent•July 23, 2018
President Donald Trump returned from a trip to Europe this week in which he insulted key US allies and caused a crisis at a NATO summit in Brussels, was met with nationwide protests in the UK, and sided with Russian president Vladimir Putin over the US intelligence community on the subject of election interference during a now infamous press conference in Helsinki.
Once back in the US, Trump on Tuesday walked back on his statements regarding Russian election meddling, stating he believed the conclusion from US intelligence agencies that the Kremlin interfered in the US presidential election, though he also said it could be “other people also”.
But on Wednesday, Trump claimed Russia is not planning future attacks on US elections, directly contradicting statements made by Director of National Intelligence Dan Coats earlier this week.
Americans think Trump is ruining their country’s reputation
In this context, many are concerned Trump is doing immense damage to America’s global standing by pushing away allies and taking the word of foreign adversaries over US intelligence agencies.
A majority of Americans (61 per cent) feel the US is less respected across the globe with Trump in the White House, according to an NBC News/SurveyMonkey poll released on Wednesday.
Meanwhile, experts warn it could take “years” for the world to trust the US again as Trump continues to attack the international institutions it played a fundamental role in building following World War Two, especially the NATO alliance and the United Nations.
‘It will take a long time for the world to trust US stability again’
David Rothkopf, a foreign policy expert and visiting scholar at the Carnegie Endowment for International Peace, warned against hyperbolic assessments of the impact Trump can have on America’s place in the world.
“Nothing is irrevocable,” Rothkopf told Business Insider. “Much of America’s global standing is based on factors that Trump won’t or can’t greatly diminish – from the vitality of our economy to our innovation, the strength of our armed forces to our history.”
But Rothkopf also noted that Trump does have the capacity to do “long-term damage to our alliances, our crucial international relationships and the international system that has been essential to our peace and stability since World War Two”.
These relationships could recover quickly, Rothkopf said, but “underfunded institutions” may take longer to recover. What will take longest to address is the “degree to which countries like China or groups of countries like the EU take the lead in our absence”.
(continued in first comment below)