I doubt Grayling will be home secretary anyway, in the event of a Tory victory. Given his comments about gay couples and B&Bs, he's clearly an electoral liability (as well as a fool).
I hope you are right but your logic is flawed. He is Shadow Home Secretary
now.
Now is election time.
Now is the time that he is a liability. After the election, if and when he is appointed Home Secretary, it will be 5 years to the next one so his Christian Right homophobia won't count for much, so he won't be an election liability then; (every other kind of liability I grant you, but not an electoral one.)