Cochran and his cronies who aided and abetted his scheme to steal this election have decided that Republicans in MS are too stupid, or misguided, or brainwashed, or zealous to choose their own candidates. Democrats have to be brought in to make sure the anointed candidate wins.
I suspect many of the Mississippi GOP politicians, like all across the South, were Yeller Dog dems until the “conservative tide” came in across the South. So cheat is in their genes.