Trump's speech after riding in the garbage truck was genuinely hilarious, especially the non-political parts. Had some profanity, but his reaction at seeing how high that first step was on the truck range true, which is why it was funny.
I can't say whether Colbert was funny or not, or if his humor transcends politics. I do know the late night market is shrinking, and even though he had the highest percentage of viewers in that time slot, there are fewer viewers. Colbert's show, by all accounts, loses money, so it's not surprising that it's being canned. If it was just Colbert being canned, they'd have a new host. That the entire show is headed toward cancelation is the telling part. That suggests the problem is more late night TV than Colbert. By now, Colbert is probably catering to his core audience, so if he'd gone "off brand" he's be apt to lose that high percentage of viewers.
It used to be that late night TV was the only thing on. I'd watch it when I couldn't sleep, usually when sick. But the last time I stayed up to take a fever reducer, I didn't watch late night TV. Instead, I watched reruns of Storage Wars. These days we have choices that didn't exist half a century ago, which means if we want to watch TV at that hour, it doesn't have to be what the networks broadcast. And I think that's what's going on with declining viewers in that time slot.