Caught this on my recent West End trip, and I enjoyed it but didn't love it. I think I wish I knew Julius Caesar better before going into this since it seems like thee are a lot of references to it, but I wasn't quite clued in on what they were. I thought the very first scene and Trump's entrance was a rather inspired bit of direction but the extended monologue in a Shakespeare-esque wording took me a bit out of it to imagine Trump being able to speak so eloquently, but I did like how they handled the later forms of direct address.
The first act was a bit slow for me, and nothing that was said there really came as a revelation or a surprise so I didn't feel super engaged (he plays a fairly minor part, but how familiar with Ted Cruz as a political figure are people overseas?), and the ending felt a little too pointed and on the nose. The second act though I really enjoyed, as it took a larger departure from what we already know/predict about Trump's mannerisms and delved more into political intrigue/morality. Despite not liking the ending of the first act, I really liked how it played into the events of the second act, which also felt a bit more Shakespearean (which for me made it more interesting).
Outside of Bertie, I agree that Tamara Tunie as Kamala and Lydia Wilson as Ivanka are the best parts of this show (I admittedly haven't really followed the press conferences/debates as much as other people so I can't speak to how accurate their portrayals are, but as actors they were quite engaging). And I agree that Joe Biden seemed underutilized here, with barely even an attempt made at a proper impression. It feels a bit like real person fanfiction but I did really like the character arcs for Kamala and Ivanka, and honestly it's just a joy watching Bertie on stage. Also, the Old Vic is a GORGEOUS theater.