One of Mr. Trump's signature policy positions is the repeal of the Johnson Amendment. At a time when there is near universal agreement that there is too much money in politics, he wants to add even more.
The short form of the Johnson Amendment is that if you are a 501(c)(3) tax exempt organization, you can not participate in politics. The basic rational is that if you don't pay, you don't get to play. It should be worth noting that enforcement of this has been fairly lax. But, for the most part 501(c)(3) organizations play nice and follow the law.
The scary part is that, if elected, this is one of the easiest goals for Mr. Trump to achieve. There isn't a cost to the tax-payer, it opens new sources of donations for the political class, and can be spun as a "Freedom of Speech" issue.
The amount of money that religious organizations can pour into politics is terrifying. There are roughly 18,000 Catholic parishes alone in the US. If each one puts in just $5,000 apiece, the Catholic Church can inject $90 Million into US politics all by itself.
Money aside, the ability to campaign from the pulpit can not be discounted.
For all of the fear that certain segments of the population have about religious laws such as Sharia, cannon law, Halakha, Hindu, Jain, etc.., allowing religious organization political power is how many parts of those religious laws would get implemented.
Nobody is going to stand up and say, "Hey, lets adopt Sharia law here". Instead, it would be a gradual process as city council members, mayors, school board members, etc... will "owe" a debt of gratitude to various religious organizations that backed them.