He does seem cowardly in certain ways, such as how he avoids confrontation by agreeing with everyone privately, even when doing so forces him to contradict himself. Some of what seems like cowardice, though, may be just a lack of empathy. He didn’t want to put himself in danger by becoming a soldier, because he’s a narcissist who doesn’t care about anyone but himself.
In any case, I don’t think cowardice explains why he hasn’t led the US into devastating, one-sided wars which he could lead from the rear, without putting himself in any danger.
Then again, as another commenter pointed out, Trump’s response to Woodward on when he knew the coronavirus was more deadly may indeed change the calculation. It’s hard to explain how Trump could think that covering up the problem would help him in the long run. He didn’t want to upset the stock market and he had zero empathy for his fellow Americans whom he was misleading into not protecting themselves against the virus.
In that case, Trump could be held responsible for an indirect kind of mass murder, for supreme recklessness which might put him in the lower ranks of the world’s brutal tyrants. Trump may be showing that it’s possible for him to indirectly kill many people while still being a coward who can’t even order his military to fulfill his depraved whims.