Although 36% is low, it's not that low. The US's two-party system means that ~40-50% are aligned with either party and approve/disapprove on GP. The real number to pay attention to is the change over time in the approval rating: https://www.cnn.com/polling/approval/trump-cnn-poll-of-polls

Trump's highest rating was ~47% when he came into office, but he was pretty stably in the low 40s until the new war. The actual drop is somewhere from ~40-42 to ~36-38 - about 10% of his base. Significant, but probably not enough to actually matter unless it drops further.