Both John Bolton and William Barr are talented hard right ideologues who thought they could separate the reactionary “good” Trump from the narcissistic man on golf cart who pursues nothing but his own whims and interests. Both of them were proved wrong and left the administration on bad terms. Both of them have been deeply critical of Trump since January 6. Bolton has remained so; Barr, on the other hand, says he will support Trump for president in spite of his innumerable shortcomings and his appalling record. Why the difference?
Personalities matter here, of course, but I think there is a deeper reason. The Trump critics who focus on his foreign policy have, with one glaring exception, continued to oppose him because they know there are no meaningful checks and balances in foreign affairs. If Trump wants to embrace dictators and surrender Ukraine, no one is going to stop him. Barr, on the other hand, probably believes the legal guardrails in the system will hold again. He is probably wrong about that.
In case you were wondering, the exception is Lindsey Graham, who values golf outings with Trump over support for democratic regimes overseas.