I'm gonna put it all out there, Donald Trump is intellectually incapable to executing long range planning of any time. Clearly Donald Trump was stomping around the White House Situation Room in a fearful snit over impeachment, until of course some oily sycophant mentioned the possibility of killing a high level Iranian Terrorism Facilitator with a drone strike. Trump immediately saw a tough homicidal stunt that would drive impeachment off the front page...he couldn't begin to conceive of any negative reprocussions from snuffing Soleimani. And since Trump is mentally deficient when it comes to information that challenges his cherished grievances, we are now on the brink of war with Iran thanks to an unsuccessful bid to get control of the new cycle.
I also don't believe that Senator Graham was briefed about anything, I think he just automatically alibis for Trump after the fact, the nonexistent legal niceties with the Congress just underscores that fact that this action was about as casually volitional as a tweet.
Alas I suspect the long range prospects her are all in Iran's Favor, they can exploit surprise and trained terrorist cadres to retaliate at will and on as carefully planned a ladder of escalation as any conceived by the late Herman Kahn. Our troops, diplomats, civilian associates everyone in the region is in terrible danger starting now, we'll be lucky to get away with a new round of hostage takings quite frankly.
I don't think Trump wants war (he seems to viscerally fear the US Military on some level, even though he lauds in very crude laughable terms for the most part) but he does want to supersede impeachment and get reelected. A war is something he could very well lose or at least lose control of, but on the other hand, he does seems to love war-like stunts.
So if John Bolton is still dreaming of Regime Change in Iran, likely Trump is the Last Person on Earth Who Will Make That Happen. I'll be curious to see if testimony is arranged at the Impeachment Trial, and if so, does Bolton testify?