In the days since the president deployed hundreds of National Guard troops and federal agents to patrol city streets, crime has continued to drop in Washington. The question is whether the trend will last.

Local politicians, along with people who study crime for a living, say probably not.

In Washington, local elected officials have called President Trump’s deployment of the National Guard to fight street crime a power grab — just a temporary show of force unlikely to produce any durable reductions in crime, since leaving hundreds of troops on the ground indefinitely is unsustainable.

“The reason that surges are not particularly effective, and are generally disfavored by crime researchers and others who look at this stuff for a living, is because it’s a resource-intensive way of temporarily reducing crime,” said Thomas Abt, director of the Center for the Study and Practice of Violence Reduction. “If it does in fact reduce crime, that doesn’t address any of the underlying conditions.”

If the president is interested in long-term solutions, experts suggested a number of other ways the federal government could help drive down crime rates in a more lasting way, from funds for training and recruitment for local officers to ideas that are less obviously focused on crime. One is something Mr. Trump himself has already floated: a $2 billion dollar spending project to spruce up Washington’s public spaces, including fixing sidewalks, improving parks and adding new streetlights.

“It’s going to be beautiful, all those lightbulbs,” Mr. Trump told reporters recently.

Lightbulbs actually do have a role to play in cutting down on street crime. Lighting up dark spaces, planting grass on vacant lots, refurbishing abandoned homes and otherwise fixing up the city landscape are widely seen as simple and effective ways for cities to reduce gun violence, backed by studies in Flint, Mich., and Philadelphia.