RIGHT NOW, THE RENTAL INDUSTRY is on quite a run. In the first quarter of this year, rents went up 4.9 percent nationally, according to Dallas-based research firm Axiometrics. The optimism flowed in apartment REITs’ first-quarter earnings calls, as well.

“All signs indicate that 2012 will be a better year than 2011,” Highlands Ranch, Colo.–based UDR CEO Tom Toomey says. Others agree. “This is one of those quarters that makes me reluctant to talk much about it, for fear of jinxing any subsequent quarters,” says Keith Oden, president of Houston-based REIT Camden. “Virtually every metric we use to monitor the conditions on the ground at our communities is either very good or excellent.”

So what could turn all of these metrics and numbers that have been trending upward for more than 24 months, now, sideways—or even backward? With the strong supply–demand situation in many markets around the country, it would take a lot.

Whether it’s pulling out residents as rents get too high, throwing a wrench into how apartments are fi nanced (and, subsequently, ruining valuations and the transaction markets), stopping the production of sorely needed new supply, or sending the economy back into recession, there are groups and people out there who could hurt the multifamily industry. Here are four:

Eric Lipar: CEO of LGI Homes

How He Could Crimp the Recovery:

There are lots of home builders out there who are trying to pull renters out of apartments. Among them, Lipar stands out for the almost maniacal fervor with which his team preys on apartment residents as potential home-buying customers. His company, LGI Homes, not only survived the recession but thrived by pulling renters out of apartments in Phoenix, San Antonio, Houston, and Dallas. Last year, it closed 627 homes, a 42 percent increase over the year before.

Lipar’s homes, with a price tag of $120,000 to $175,000, are priced for first-time home buyers—those people who currently reside in apartments. “Ninety-nine percent of our customers are renters,” he says.

How is Lipar, whose background is in sales and marketing, able to reach these renters? Good, old-fashioned snail mail. He may be keeping the U.S. Postal Service in business by sending out about 200,000 pieces of mail a week. He’s on track to send out about 10 million mailings this year.

“Anyone who pays rent within 20 miles of one of our communities gets a flier or direct-mail piece every four or five weeks,” he says.

On the flier, Lipar has a simple message—why rent when you can own? In Houston and Dallas, for instance, markets where rents have risen 5.1 percent and 5.7 percent, respectively, over the past year (­according to Axiometrics), he pitches affordability, advertising a monthly payment of $629 to $729 (the principal and interest on a home). He says his average customer is paying $800 to $1,100 a month in rent when he or she decides to buy a home (that’s, of course, if the buyer can get a loan, which Lipar admits is still a roadblock).

“If you came from an apartment in North Dallas, paying $900 to $1,000, and if you went to our community and saw what you get for $900 to $1,000 a month, there’s no comparison,” Lipar says. “We win that battle 99 percent of the time, logically. That doesn’t even count the emotional aspect of homeownership, and family and everything that goes along with it.”

As Lipar’s success proves, the rental industry may be enjoying quite a run right now, but aggressive home builders can’t be counted out. And, as single-family pricing stabilizes and rents rise, the competition for customers promises to grow even more ­intense.

Multifamily Moral:

Make a plan to combat home sellers now. Especially as rents run up, they’ll pound the market with the message that monthly costs to own beat renting.

Tim Geithner: U.S. Secretary of the Treasury

How He Could Crimp the Recovery:

Several noted officials in Washington could spoil multifamily’s party with one seemingly small move, but ultimately, Secretary of the Treasury Tim ­Geithner may have the best shot of mucking up the waters for apartment owners. The reason is simple—Treasury controls 79.9 percent of Fannie Mae and Freddie Mac. Eventually, there will be a big decision to be made about the future of the two government-sponsored enterprises (GSEs). And if President Obama is re-elected, Geithner (or whoever is running Treasury at the time a decision is made) will be an inevitable prime force in the deliberations.

Make no mistake, the shuffling of those cards will be vital to apartment owners everywhere. When the credit markets froze in 2008, the only lenders open for business to the industry were the GSEs. In 2009, they handled 85 percent of the origination volume in the business. In 2011, that number was 57 percent. Despite all the talk about insurers providing debt and the return of commercial mortgage-backed securities (CMBSs), the multifamily business is still hugely reliant on the GSEs.

So, if the Treasury secretary doesn’t recognize the importance of the GSEs to the apartment market and decides that a one-size-fits-all solution for housing finance is the best way to go, the fallout could be ­explosive: The cost of borrowing would rise, asset values could plummet, and a burgeoning transaction pipeline could grind to a halt.

Multifamily Moral:

Get behind the National Multi Housing Council’s ­efforts to educate elected officials and regulators about the need for, and strong performance of, a stable liquidity backstop for multifamily.

Angela Merkel: German Chancellor

How She Could Crimp the Recovery:

As European elections usher in new leaders such as France’s François Hollande and defeat austerity hawks, eyes turn to German chancellor Angela Merkel, who has ruled out renegotiation of a European Union pact calling for tight budget controls. But the victory of ­Hollande, who has called for new policies to boost ­European economic growth, shows that voters in some countries reject the stern measures Merkel supports.

What does this mean for the everyday U.S. apartment owner? Well, if Merkel clings strictly to the original EU pact and doesn’t OK another bailout, many worry that Europe could plummet into recession if the economy deteriorates in countries like Spain and Portugal. Many think Merkel’s rigidity on cutting entitlements and other long-standing expenses pushes Europe further into crisis.

“If Merkel decides to get really, really tough, or they throw Greece out of the European Union, or someone reneges on commitments, it could send Europe into ­recession,” says one capital markets watcher.

In this global economy, that could derail the fledgling American recovery. Some say the effects could be similar to those of the fallout from the Lehman Brothers bust in 2008. In the following year, effective apartment rents fell 6.2 percent and occupancies declined 1.2 percent across the country.

Several things have to happen for Merkel to thwart the U.S. apartment industry. But if she doesn’t stop Europe from falling into an economic abyss, the results could be calamitous. It could cost American jobs. And, as everyone knows, jobs are the lifeblood of the apartment business.

Multifamily Moral:

Hope for the best, but prepare for the worst.

Laura Karvala: Realtor and Organizer of Concerned Citizens of New Berlin

How She Could Crimp the Recovery:

Not everyone out there is trying to build ultra-­expensive units. But local NIMBY (short for “not in my backyard”) groups can present obstacles that not only make it more difficult to provide sorely needed affordable housing but also heap costs on prospective projects.

Usually these local, “Concerned Citizens” groups express concerns with a development’s impact on parking, utilities, schools, and the like. In New Berlin, Wis., Realtor Laura Karvala’s Concerned Citizens group initially killed a 180-unit project from St. Louis, Minn.–based MSP Real Estate. In rejecting the bid, the city argued it had initially approved a different project under another entity, according to www.newberlinnow.com. MSP sued, citing racial discrimination and violations of the Fair Housing and Americans with Disabilities acts.

Eventually, the city came to an agreement with MSP, and the project, City Center at Deer Creek, began construction in September 2011, according to the Milwaukee Business Journal. But the initial success of Karvala, who claimed that opposition to the project was due to issues such as underground parking and child safety, shows that a determined local group with a strong leader can stop ­development in its tracks.

The costs associated with NIMBY efforts are real, say affordable housing developers and advocates. NIMBYs can stall a project, forcing a developer to spend money to go back for appraisals and other due diligence and possibly lose tax credits.

Multifamily Moral:

Multifamily developers need to anticipate community push-back and develop new ways to win over local movers and shakers.