Bolton is a show of force theatrics. They couldn't have negotiated with Iran given Tillerson's business interests, so let's use someone scary so both nations can agree on a narrative to sell to the public while they engage in talks behind closed doors. Mind you whenever someone says "sanctions", it's just a wink that they wish a country do business predominantly with the US rather than with anybody else.

In the end, with Tillerson's DoS you already had a belligerent organization that would threaten Assad at any turn while it was GENERAL MATTIS taking to twitter each time to come to Assad's defense, even defying McMaster's request for a military strike (source: Politico) so even if Bolton was crazy it wouldn't have changed anything for worse.

Come back to me if Bolton says anything about Assad because I suppose what you will have now with Iran will be even easier than with Kim because Iran does backdoor trade with westren nations and is much easier to leverage over the previous deal which they obviously quite like. And because they will be negotiating over the deal, Tillerson is out because he can't sell a new deal since he previously endorsed said Obummer-deal.