In the mid-1960s the Vietnam War became an important issue. The PSP was heavily involved in opposition against the American intervention. It was the first party to pay attention to the war and it was involved in the organisation of demonstrations, rallies and teach ins. The monarchy also became an issue as Crown Princess Beatrix would marry Claus von Amsberg in 1966. The PSP used this opportunity to voice its support for a republican constitution. In the same year the CPN-dissenters of the SWP joined the PSP. The PSP held on to its four seats in the 1967 election. In 1969 Gortzak, previously leader of the SWP returned as MP: now for the PSP.