Having dealt with some people who are bipolar/manic, I am not absolutely sure he was in mania. Some things certainly point towards it and we all agree they like mania and not taking meds or going off them. But with all the new designations via personality disorders, getting the analysis right is not a perfect science.
Most of the people I have seen in mania are either deeply or creatively introverted or all-out wild, be it promiscuity, living as someone else, etc.
I think a case can be made that he did not meet those standards and seemed somewhat grounded for his personality. OTOH, he was in the White House and had the floor but many manics cannot go into mania on cue, nor when scheduled to appear. So with that said, I am not certain we can say in an authoritative way that he was indeed manic and if so, examples which are not blanket statements are welcomed. FWIW, I am not saying there is not a possibility, just that it is not cut and dry per my studies.
I agree that is is often somewhat of an educated guess when putting a label/diagnosis on someone from a distance who is not very well know in person. That said, he has been behaving somewhat strange lately, like his impromptu speech after SNL and other occasions.
According to the Diagnostic and statistical Manual of Mental Disorders, Fifth Edition (DSM-5) a manic episode is defined as:
B. During the period of mood disturbance and increased energy or activity, three (or
more) of the following symptoms (four if the mood is only irritable) are present to a significant
degree and represent a noticeable change from usual behavior:
1. Inflated self-esteem or grandiosity.
2. Decreased need for sleep (e.g., feels rested after only 3 hours of sleep).
3. More talkative than usual or pressure to keep talking.
4. Flight of ideas or subjective experience that thoughts are racing.
5. Distractibility (i.e., attention too easily drawn to unimportant or irrelevant external
stimuli), as reported or observed.
6. Increase in goal-directed activity (either socially, at work or school, or sexually) or
psychomotor agitation (i.e., purposeless non-goal-directed activity).
7. Excessive involvement in activities that have a high potential for painful consequences
(e.g., engaging in unrestrained buying sprees, sexual indiscretions, or
foolish business investments).
I believe to see, at least, three of these symptoms displayed during his Oval Office speech.