President Donald Trump and California's top politicians are sniping at each other again, this time over the issue of homelessness.

On Monday, Trump gave an interview in which he decried the problem of homelessness in a number of cities—mentioning New York, San Francisco, and Los Angeles by name—while saying that the federal government might have to "intercede."

"It's a phenomenon that started two years ago. It's disgraceful," Trump told Fox News host Tucker Carlson, saying that cities with large homeless populations were "usually sanctuary cities, run by very liberal people and the states are run by very liberal people."

It's obviously wrong for Trump to say that homelessness is an issue that started two years.

Were that true, it would have meant that very liberal people like President Barack Obama and California Gov. Gavin Newsom had fulfilled their promises to end homelessness, at least for a time. Obama pledged in 2010 to end chronic homelessness by 2015. Newsom, when he first became mayor of San Francisco in 2004, said he'd do the same by 2014.

Newsom himself shot back at Trump on Tuesday.

"You'll have to ask him what 'interceding' means. If interceding means cutting budgets to help support services to get people off the street, he's been very successful, at least advancing those provisions," the governor told the Los Angeles Times.

Trump has, in fact, not been very successful at advancing cuts to federal homelessness funding. Though his administration's budget proposals have called for cutting spending on the Department of Housing and Urban Development's (HUD) homeless assistance grants, spending on that program continues to increase every year.

Los Angeles Mayor Eric Garcetti, while decrying Trump's comments as "cheap shots", has also said he supports having the federal government "intercede"—at least financially—in addressing the city's homelessness problem.

On Monday, Garcetti said he would be leading coalition of mayors to lobby Congress to pass the Ending Homelessness Act—introduced in March by Rep. Maxine Waters (D–Calif.)—which would spend an additional $13 billion over five years on new and existing federal homelessness and housing programs. To build support for the legislation, Garcetti has said he will lead a rally in Washington D.C., testify before Congress, and get more co-sponsors on board.

Were federal funding increased further, it's still an open question as to how much that extra money would help people without shelter get into more permanent housing. In places like Los Angeles, there's been a major increase in state and local spending on homelessness alongside a growing number of people living on city streets.

In 2016, Los Angeles voters passed Proposition HHH, a $1.2 billion bond measure city officials said would help construct 10,000 new units of housing, of which 7,000 would be "supportive units" reserved for the formerly homeless, within a decade.

The city is projecting that about two-thirds of those funds will only pay for about half the number of units it was promising. The city has committed $810 million of Prop HHH money, which it is expecting to help subsidize the construction of 5,388 units. Only about 4,100 of these will be supportive units, the rest being reserved for currently housed low-income people.

So far, no Prop. HHH units have been completed, although some 150 (including 100 supportive units) are expected to open by the end of 2019.

Realizing they will likely not have enough money to fulfill their 10,000-unit promise to voters, Los Angeles politicians have started looking for ways to stretch remaining funds as much as possible.

In January, the Los Angeles City Council set aside $120 million of Prop. HHH money for a pilot program that would fund cheaper, non-conventional forms of public housing construction. In late June, City Council member Mitch O'Farrell asked the state to match the $1.2 billion bond measure Los Angeles voters had already passed.

Last week, state lawmakers agreed to spend $650 million on homelessness aid to local governments, earmarking $250 million of this for the state's 13 largest cities. How much Los Angeles will get from this pot hasn't been determined yet.

Judging by Garcetti's aggressive solicitation of Congress for funds, it won't be enough.

And even if Los Angeles were able to secure enough federal and state money to complete its goals under Prop HHH, this new housing would shelter only a small number of the city's surging homeless population.

A 2019 count of the city's homeless population found that it had grown by roughly 16 percent to 36,000 people. In Los Angeles County, the homeless population totaled nearly 59,000. This growth is despite the fact that the city spent $619 million on homelessness—including $442 million in Prop HHH dollars—in 2018. It received $85 million in state aid in the same year.

One possible reason for the increase is that the same restrictions on development that make housing more expensive in Los Angeles—and thus exacerbate the city's homelessness issues—also make it harder to build the supportive housing the city is saying it needs to address homelessness.

Long approval times, sky-high land and labor costs, and a permitting process that gives NIMBYs ample opportunity to slow or stop new development all hamstring the city's attempts to build new housing for the homeless. In one particularly egregious case, Metro—the Los Angeles area's transit agency—spent over a decade trying to get approval to build supportive housing on land it owns in the city.

That combined with the normal inefficiencies we would associate with the public sector ensures that Los Angeles will continue to spend a lot of money on not that much housing.

To Garcetti's credit, the mayor has thrown his support behind a state bill that would exempt emergency shelters and Prop. HHH-funded projects from laborious environmental reviews, which should speed up their delivery. The Trump administration has also proposed reducing federal regulations that drive up the costs of housing. Still, absent wider reforms, rising unaffordability will continue to push more folks onto Los Angeles' streets.

By demanding more federal aid to address homelessness in Los Angeles, Garcetti is asking for taxpayers to subsidize this dysfunction. Instead, the mayor should look at making deeper reforms to the city government he runs.