Nothing good was ever going to come from having John Bolton as National Security Advisor, and fortunately Trump rejected almost every major recommendation that Bolton made during his entire tenure. If Trump had gone along with Bolton's agenda, we would probably be at war right now.
Being so close to the levers of power and being unable to move his agenda forward time after time was very frustrating for Bolton, and since he was fired by Trump he has been on a "revenge tour". But would Bolton go so far as to completely betray Trump by becoming the "second whistleblower" regarding the controversial phone call with the president of Ukraine? There is now a lot of speculation among conservatives that this could be the case, and so far Bolton has not publicly denied being the ""second whistleblower". That doesn't mean that Bolton is guilty, but if I was President Trump he would be the number one suspect on my list.