Trump’s decision to renege on the nuclear deal was a terrible unforced error, and the process that led to that decision  is no less worrisome:
Even if Mr. Mattis had wanted to fight for the deal, it is not clear how much he would have been heard. Mr. Bolton, officials said, never convened a high-level meeting of the National Security Council to air the debate [bold mine-DL]. He advised Mr. Trump in smaller sessions, otherwise keeping the door to his West Wing office closed. Mr. Bolton has forged a comfortable relationship with the president, several people said, channeling his “America First” vocabulary.
Bolton’s handling of the run-up to Trump’s decision on the nuclear deal shows that he isn’t interested in presenting a range of opposing views to the president and the president is content to let Bolton limit the information he receives. One of the reasons to be worried about having Bolton as National Security Advisor is that he will not be an honest broker when it comes to presenting the president with all the facts. That worry was obviously well-founded. Because Bolton is an ideologue and has extremely hard-line views on Iran in particular, he isn’t going to allow the president to hear views that contradict his own, and that means that Iran policy in particular and U.S. foreign policy in general is going to become more aggressive and ideologically-driven than they already were.
This is all the more disturbing because of reports  that Bolton’s NSC is circulating plans to foment regime change in Iran:
The plan, authored by the Security Studies Group, or SSG, a national security think-tank that has close ties to senior White House national security officials, including National Security Adviser John Bolton, seeks to reshape longstanding American foreign policy toward Iran by emphasizing an explicit policy of regime change, something the Obama administration opposed when popular protests gripped Iran in 2009.
The regime change plan seeks to fundamentally shift U.S. policy towards Iran and has found a receptive audience in the Trump administration, which has been moving in this direction since Bolton—a longtime and vocal supporter of regime change—entered the White House.
It doesn’t come as a surprise that talk of regime change in Iran has increased since Bolton took office. Bolton is a longtime advocate for the Mujahideen-e Khalq, a deranged totalitarian cult that he would like to install as the next government of Iran, and he has made no secret of his desire to topple the Iranian government. It was just a matter of time before he started trying to make this official policy.