I first heard this watching Rick Stein's cooking show in the Basque Country, but I have seen it more and more lately, particularly around USA's Columbus Day.
Leif Ericksen I understand, and I feel the case has been made with good evidence and fair consensus amongst historians. But upon what is based the claim that Basque fishermen knew America through cod fishing pre-1492?
Where does this belief come from?
I would love a bit more insight into this question as well.
In the meantime, this thread answered by /u/Flavored_Crayons seems to have the most thorough answer I could find in the sub archives.
https://www.reddit.com/r/AskHistorians/comments/1hg1g8/basques_in_north_american_prior_to_columbus/