Trump Tower, the building that President-elect Donald Trump calls home, bills itself as "one of the world's elite luxury residences, catering to public figures, athletes, celebrities and other affluent sophisticates."

These days, some other people have taken up residence there as well: Secret Service agents.

Trump has said that his family won't move into the White House right away and will remain, for a few months at least, in the world-famous steel-and-glass office and residential building where they occupy three floors.

Even after his family makes the move, Trump seems likely to be a regular visitor in Manhattan, where he has lived for decades.

For the Secret Service, that means setting up a vast intelligence and surveillance operation inside the building.

"Essentially what you have to do is make Trump Tower as secure as the White House," says former Secret Service agent Jonathan Wackrow.

To do that, the Secret Service will almost certainly have to lease space inside the building, which is partly owned by Trump himself, giving the president-elect an opportunity to make money off the very agency assigned to protect him. It will probably have to do so at Trump's Florida resort, Mar-a-Lago, as well.

Wackrow, who is now executive director of the risk assessment company RANE, says this isn't at all unusual. The agency leased space in Crawford, Texas, where former President George W. Bush owned a ranch, and in Chappaqua, N.Y., the home of Bill and Hillary Clinton.

"We do it at a lot of facilities. Anytime the federal government is taking private space, it's logical for there to be a rental fee around that," Wackrow says.

The difference is that Trump Tower is located in a ritzy shopping district in Midtown Manhattan, one of the most expensive places on earth, so rents there are likely to be a good bit higher than in Crawford.

Just how much higher is hard to say.

Secret Service officials are still trying to assess what they need to protect the Trumps and what the agency's "footprint" will be inside the building, so they didn't want to comment for this story.

The Trump campaign was paying $35,458 a month to lease space in the building as recently as last March, but the price increased nearly five-fold by July. Critics said the increase — to a monthly rent of $169,758 — was a way of fleecing donors at a time when they were increasingly contributing to Trump's campaign.

Steve Siegel, chairman of global brokerage at the giant commercial real estate firm CBRE, says office space in Trump Tower typically rents for about $70 a square foot, which amounts to $700,000 a year for 10,000 square feet of space. That's less than in premium properties such as the GM Building, which can go for $95 to $190 per square foot.

It's not that there's anything wrong with Trump Tower, which is an attractive building with high ceilings, usable space and plenty of light, Siegel says.

But much of Trump Tower consists of condominiums. Only the first 26 floors of the 68-story building are set aside for offices and retail stores, and some of that has been occupied by Trump's own businesses.

Not enough space is left over for really big companies, and that lowers the price that the building can fetch, Siegel says.

Major tenants also prefer to put their own names on buildings, and Trump Tower is already named for Trump, Siegel notes.

Siegel adds that the presence of the Secret Service could actually end up hurting the building's value. Already, police have had to seal off the streets around the building, requiring anyone who lives or works in the building to pass through security checks.

"I just passed the building now and they were three deep and barricades and police everywhere," he said.

While some people may feel safer as a result, a lot of potential tenants won't want to put up with it.

"I don't think I could put a tenant in there that would be comfortable with the security measures that are required by the president-elect living there and having his offices there," Siegel says.

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