kat kid, these are not real losses! they are fictional, or at least some sizable proportion of them is almost certainly fictional. trump is a real estate dude, he owns a lot of real estate and the tax code just happens to hugely advantage real estate. property owners can write down the value of their property as a depreciating asset even though it is actually appreciating in value and generating a growing revenue stream. they can shelter their income, often up to the sale of the property, which may never come.
i have no problem with the offsetting of income with losses, or with extending those losses into future years, but only genuine cash losses, not paper losses. there are a lot of fixes for this, but trump is not proposing any of them.