They don't. Not even close. Portland, like Washington, is over the tax. They would have to send out at least $20.73M to bring in Porter and then pay massive luxury tax on him. The way I see it, the only way that Portland has a chance to do this would be sending Harkless/Leonard/1st for Porter - but that would only save Washington about $11M total, and Washington would still have to pay about $8M on Porter's trade kicker. So I don't see how Washington wins on that deal.
I mean, I guess Portland could go with Harkless (not expiring)/Aminu/Curry/Baldwin/1st which would add another $11M or so to Washington's cap relief next year, but that would push the Blazers to $142M for next with three roster spots to fill. Portland doesn't make much sense to me.
To me, the bottom line is that as best as I can tell, the Kings are the only team that can give Washington serious cap relief - there's a way for us to take on both Porter AND Mahinmi, and it wouldn't really hurt us for next year since we're stacked with young guys and have $37M in expiring contracts. We'd probably demand a bit more out of that - at least a pick - but if Leonsis actually cares about getting under the tax, we're the team to help them do it. If they don't want to, hey, it's their money.