That's is not "clear" at all. I'd suggest that's mostly just your subjective lens. Looking at the Republican party machine as a whole, they seem far more scared of Bernie and Warren than Biden.
As much as they would love to face Sanders and simply frame the Gen as a referendum between Socialism and Capitalism, they are anticipating a more realistic scenario of facing Biden, who is beating Trump in his own internal polling. That could of course change down the road but that’s how the Trumpsters see it.