I wouldn’t get too hung up on this. I watched a bit of the debate and it wasn’t just a bit stuttering. Biden was incapable of articulating points. He repeatedly referred to the wrong terms and numbers. He often looked like a lost elderly man that had wondered onto the stage. Democrats are mental to put him forward for a second term. Biden has been an effective orator in the past despite his stutter. I wouldn’t be surprised if your dads comment was more about Biden struggling to generally figure out what to say what than a few blocks or repetitions.