I disagree with this. The US has left the table on climate change, global trade, world health and many other matters. That has significant effects on many countries.
Australia is currently getting slayed by China in trade. They have banned imports of our beef, and thermal coal, and now wine, largely for our standing by our alliance with America, and America is an empty chair at the WTO right now.
Then there's the influence of the role of the US president. Obama was a worthy role model. Trump is the antithesis of that. The influence this has on people spouting absolute shite is enormous. The lessons of trumps success are very damaging to the motivation of those who strive to do good work and believe that facts matter, and that experts should not be dismissed out of hand with an eye roll. The world's most powerful democracy is failing right now and that is significant and alarming.