President Obama is doing a question-and-answer session today hosted by Zillow.com, a website that focuses on one of the president's "cornerstones" of a strong middle class: home ownership. To bolster enthusiasm for the session, Zillow put a dollar value on Obama's current residence, estimating that it would sell for $319 million, and rent for $1.8 million a month. Which made us wonder: How long could various presidents and presidential wanna-bes afford to rent the White House?

That monthly rental is a hefty sum. Even in deep-pocketed D.C. those bills would add up. (Not that this should be considered a scientific valuation, of course.)

Past contenders

Al Gore
Net worth: $200 million
Number of months of rent: Nine years, three months

Had Gore won in 2000, he would have started paying rent in January 2001. Meaning that, democracy aside, he would only have had to move out in April of 2010.

Of course, Gore's net worth is largely a function of what he did instead of being president: selling Current TV, for example. When he left office in 2001, he was worth only $1.7 million — not enough for even that first full month.

Mitt Romney
Net worth: $250 million
Number of months of rent: Eleven years, seven months

Had Mitt Romney won last year, he'd have enough to stay in the building until August of 2024. If he could manage to get by without a car elevator.

John McCain
Net worth: $15 million
Number of months of rent: Eight months

McCain is lucky he didn't win the presidency in at least one sense. It would have been awfully frustrating to have spent all that time campaigning just to move out in September 2009.

If he were humble enough to let his wife Cindy chip in, dipping into her inheritance, he'd have $100 million at his disposal — enough for another four-plus years.

Barack Obama
Net worth: $7 million
Number of months of rent: Four months

The president ran out of rent money in May, 2009. We're looking into how he's managed to remain living at 1600 Penn.

2016 contenders

Chris Christie
Net worth: $2.8 million
Number of months of rent: Two months

Christie wouldn't last very long in the White House, but Jersey is a fairly short commute.

Rand Paul
Net worth: $1.2 million
Number of months of rent: A few weeks

Of course, Paul would probably eschew the big government trappings of the White House, preferring instead to live in a second-floor walk-up in Columbia Heights.

Marco Rubio
Net worth: $280,000
Number of months of rent: Zero, basically.

Contributors to a Rubio for President campaign might also be asked if they have spare bedrooms.

Hillary Clinton
Net worth: $31 million
Number of months of rent: One year, five months

That short stint wouldn't faze Clinton, of course. She's already lived there eight years.

Incidentally, you know who should run for president by this metric?

Darrell Issa
Net worth: $745 million
Number of months of rent: 34 years, six months

If Darrell Issa won the presidency in 2016, he wouldn't need to move out of the White House until July 2051 — at which point he'd be 97 years old.

Historic residents

Abraham Lincoln
Net worth: $1 million
Number of months of rent: A few weeks

This is probably why he was so depressed.

Franklin Roosevelt
Net worth: $60 million
Number of months of rent: Two years, nine months

Only about ten years less than FDR actually spent in the residence.

George Washington
Net worth: $525 million (!)
Number of months of rent: 24 years, four months

Washington could have entered the White House In 1789 and not left until 1813. Granted, it wasn't built until 1792, but at least Washington would have escaped about a year before the British burned it down.

All of this is simply speculation. In reality, of course, the White House is priceless, and cannot be bought or rented at any price.

Just kidding. It costs $1.072 billion.

Photo: Obama has some guests over. (AP)