The only reason not to kill Soleimani is if you believe doing so would likely result in greater evils. I’m not privy to the current or best intelligence, but my immediate worry is that Iran does have options for escalation at a level that will be difficult for us to match. Namely: that Iran can up the pressure in nations that Americans are tired of fighting in already. If Iran has an ability to disrupt the oil trade, they can also get into Trump’s mind ahead of the election. Gas prices will matter to him.
My other fear is that in the Middle East, Trump’s sometimes confused policy — are we in or out of Syria?– ends up defaulting toward the kind of drift we saw in the Afghanistan papers. Missions and priorities multiply without ever being accomplished when the public accepts the war as mere background noise.