 It'll be a chance for the Prime Minister to assess Joe Biden's performance and ponder, perhaps, the possibility of dealing with a very different president in a matter of months. The UK's role as a cheerleader for Ukraine could be trickier if Donald Trump returns to the White House. Potential challenges in Europe, too. Labour speaks of a reset. But if Marine Le Pen's right-wing national rally wins the second round of France's parliamentary elections on Sunday, cooperation on issues like migration could be more complicated.