Boris Johnson has clearly identified his brand of populism with Trump’s. The British are worried that this will damage their relationship with the US after Trump’s defeat and departure. Is their concern justified?
No. Unlike, say, Netanyahu, Boris never crossed the line by openly advocating for Trump’s re-election. In addition, he took positions on issues like climate change and Iran that conflicted with Trump’s. Finally, the links between the two nations are very strong. They will survive the transition easily.
The better question is whether the UK will have the same degree of influence on the US, regardless of who is in power, after Brexit. The most likely answer is no. The UK was a useful cultural and ideological bridge between the US and the rest of the EU; in less than a month, that will be gone, and the UK will find its new isolation to be less than splendid.