he did randomly decide to bomb Soleimani

It wasn't random. It was to appease the more bloodthirsty morons in Washington, who got angry when the impending war with Iran got scrapped because Iran proven they are able and willing to defend themselves. Remember how Trump and Pentagon were like 11.59 on war clock and suddenly stopped and shut up about it after Iran shot down that super drone with old Soviet missile? Right after that they even sacked Bolton which lead him to publish hilarious book where he accuse Trump of being the most sane guy in entire Rep party.

But the hawks needed to get the last word so they at least murdered Soleimani, as a treat. Some people maybe believed it will trigger the war anyway, but Iran is more restrained than them so it didn't.