President Trump blasted John Bolton, his former national security adviser, in a tweet on Wednesday, saying, "frankly, if I listened to him, we would be in World War Six by now."
The president's ire comes as Bolton and a leaked manuscript of his upcoming book are at the center of the U.S. Senate's debate on whether to call witnesses in Trump's impeachment trial.
Bolton's book claims Trump told him that aid money for Ukraine was contingent on the nation investigating the Biden family and other Democrats involved with Ukraine.
Trump denies there was any tie between the aid and potential investigations.
Senate Democrats are pushing to call Bolton as a witness in the impeachment trial, although he did not testify during impeachment proceedings in the House of Representatives. Many Republican senators are opposed to calling witnesses and question why Bolton did not testify before the House.
? As of Tuesday, Republicans did not have enough votes to block the inclusion of witnesses in the trial, said Senate Majority Leader Mitch McConnell (R-KY).