In the years before 1940 he fulfilled a number of offices in the NSB at the local level, and during the war proved himself a fanatical Nazi, adhering to the ideology of Meinoud Rost van Tonningen.
This was the first and largest of Dutch organizations of convicted collaborators; an attempt at resurrecting the NSB under the transparent moniker NESB, or Nationaal Europese Sociale Beweging, was unsuccessful.
[9] His activities with the NESB led to an arrest in 1953, when he and Paul van Tienen were sentenced to two months' imprisonment for running an organization considered a successor to the NSB.
[10] After the NESB was dismantled Wolthuis ceased having any importance in far-right parties, though he remained involved with organizations that supported veterans of the Eastern Front.
With Hartman, he played a never fully explained part in the 1952 escape of seven convicted war criminals from the Koepelgevangenis in Breda, including Klaas Carel Faber.