As a father, Papa is...
In Jeanne Wakatsuki Houston's novel Farewell to Manzanar, the author/narrator explains that her father had always served his role as family patriarch with true honor. After all, he was a hardworking man who comes from a good family and who has great, strong values.
As a father, Papa is happy to continue his Japanese traditions at home, but he is also aware of the need to fit in, in a way that the family does not get labeled. This said, the time spent at Fort Lincoln must have been a huge shock to Papa. The little dignity that Japanese families could afford after the events of 1941 would have made things twice as hard for heads of families.
The narrator says as much when she describes Papa's physical looks once he returns from Ft. Lincoln. Papa returns in September, 1942 after being gone for nine months:
He had aged ten years. He looked over sixty, gaunt, wilted as his shirt, underweight, leaning on that cane and favoring his right leg.
As far as his behavior, Papa was back giving commands and being the lead decision-maker of the family. However, his demeanor was off. The remaining family members could sense that, even though their lives had been rattled, the one person who gave them a sense of protection had altered greatly:
He was not the same man. Something terrible had happened to him in North Dakota.
First, Papa's nerves are rattled to the point that he no longer could control his anger. This causes a lot of fighting and shouting including physical violence. He also becomes a very heavy drinker, and it is the combination of the trauma from Ft. Lincoln, the alcohol, and the frustrating nature of the situation going on that leads him to, essentially, lose his self-control:
He terrified all of us lurching around the tiny room cursing in Japanese and swinging his bottles wildly.
Therefore, Ft. Lincoln and his experiences in the camp greatly affect Papa.