If the Dems had a single candidate, this might be more plausible. But, they are in their own internecine fight. How many Republicans are crossing over to vote strategically? Probably a statistical number approaching zero.Some traditional democrats genuinely want Trump to win, but also a lot of Democrats are voting strategically.
I haven't seen this quantified anywhere, and I haven't heard anything like this among my Democrat friends. (Of which, there are actually more than 2.) If there are Dems crossing over for strategic reasons, then they are fools. They should be getting their own house in order.