Natural disasters stress systems, exposing weak points.

Among the worst in modern times was Hurricane Maria,which hit Puerto Rico in September. It not only exposed the island's neglected infrastructure and the federal government's failure to respond adequately, it has opened up fault lines in Philadelphia.

The hurricane washed out roads and bridges, and shut down power and communications. In the days following the storm, thousands fled the island for the mainland.  An estimated 2,000 came to Philadelphia, and now, about 50 families are seeking Philadelphia Housing Authority units.

The federal government is only offering permanent housing support in Puerto Rico, where the disaster occurred. If displaced people want permanent housing off the island, they're going to have to get help from state and local officials, according to a Federal Emergency Management Agency spokesman.  Those temporary shelter supports run out on March 20.

Meanwhile, the disaster is pitting two desperate groups against each other and exposing yet another weakness — Philadelphia's lack of affordable housing.

There isn't enough decent affordable housing for the people who already lived here. PHA houses about 81,000 people and says about 85,000 more are waiting for apartments. The depth of the affordable housing crisis could get even worse if President  Trump succeeds in cutting $90 million from the agency.

Brian Abernathy, city first deputy managing director, says the city is hesitant to put evacuees into housing that so many Philadelphians have been waiting for so long to get.

PHA can provide housing to evacuees who can prove they were displaced by a federally declared disaster. PHA's rule on that is very clear. It grants "super preference" to those who get a FEMA referral. That means they jump to the top of the waiting list. However, even if the 50 Puerto Rican families got priority, they could wait weeks or months before apartments become available for them.

Making matters worse is that the families may not even be able to get those super FEMA referrals. The city says those families have to rely on yet another bureaucracy called a long-term recovery committee, headed by a single nonprofit organization. These committees help find permanent housing, jobs, and job training for evacuees. They receive assistance from national and local religious and civic organizations.

That hasn't happened here because factions in Philadelphia's Latino community can't agree on which nonprofit group would head the committee.

The Latino community has shown extraordinary generosity to Puerto Rican evacuees, but  that help shouldn't be undercut by politics.

Fundamentally, the federal government should take responsibility for helping these disaster victims. But it won't, which leaves the fates of these families in the city's hands.

To be sure, the city has done a lot to fill in the gaps left by FEMA's limited assistance. It opened a disaster assistance center between October and December. It helped 2,000 evacuees apply for FEMA aid as well as other services, including food stamps and temporary financial assistance.

Increasingly, it is left to cities to solve big systemic problems; in this case, Philadelphia should make sure it exhausts all possible solutions, even short-term ones, to keep these 50 families from drowning in a sea of red tape.