Vice really is trying to say that because Republicans are too mainstream to attract the extremists that this is a problem with and for the Republicans. The only justification for this sort of twisted logic is that it’s an election period and Vice has decided to be party partisan rather than journalists.
Try the logic the other way. Would you be happier or more worried about the Democratic Party if there were 20,000 communists who were not members of the Democratic Party because it was too mainstream? Assuming, of course, that there actually are 20,000 communists left who have not already joined the Democratic Party.