After Soleimani was killed and a war was nearly started with Iran in January 2020, there was still an “oh shit” moment from the Trump government and they quickly walked back and prevented a war from being escalated.

You got the order wrong, they first backed off from war around september 2019, and then assassinated Soleimani as a last word and consolation prize for hawks. The actual reason they backed off was that Iran demonstrated both will and ability to defend itself by series of force shows and shooting down the best US drone with old Soviet missile - which also shown pentagon bonzos that the war might be way harder than they though.