Trump didn't start Leif Ericsson day.
https://en.wikipedia.org/wiki/Leif_Erikson_Day
On September 2, 1964, Congress unanimously authorized and requested the President to create the observance through an annual proclamation.[13][14] Lyndon B. Johnson did so that year,[15] as has each president in the years since,[16][better source needed] often using the proclamation to praise the contributions of Americans of Nordic descent generally and the spirit of discovery.[17][18]