Being able to help pick and choose politicians, for one. If the Catholic Church were to gain another 15 million faithful Catholics who could be told, in a manner of speaking ,as to who to vote for that would have an effect on which politicians could be chosen.
It could cause politicians, on both sides and at all levels, to have some consideration for policies that are favourable to the Catholic Church.
He’d be nuts to expect them to be able to steer a crowd of that kind to be anything other than Democrat, though.