Despite the concerns of some Democratic leaders and city officials in Chicago, the state of Texas has not sent buses filled with migrants to the city this week during the Democratic National Convention.

In fact, no buses have been sent by Texas anywhere for nearly two months, according to state data obtained by The New York Times, and interviews with state and local officials in Texas. The last bus left the border near El Paso on June 27 carrying 50 migrants to New York.

The reason for the lack of buses, Texas officials said, was not that the program had been halted.

There have simply not been enough migrants to send.

The absence of buses began after the Biden administration issued an order in June that sharply limited the number of migrants released into the country after crossing the border illegally.

The order, which has been opposed by civil rights groups, cut down on the number of crossings and effectively eliminated what had been a potent political tool used by Gov. Greg Abbott, a Republican, to pressure Democratic city leaders into paying attention to the border.

Since the busing program began in 2022, Texas has transported more than 120,000 migrants to Democrat-led cities, including Chicago, New York, Washington and Denver. Shelters and city services were often overwhelmed, prompting Democratic officials to plead for federal assistance and leading some to temper their support for newly arrived migrants.

But the strains have eased in recent months, particularly since the Biden administration’s change in policy, which capped the number of asylum-seekers at the U.S. border.

“As of yesterday, there was no one in our emergency shelters,” said Jon Ewing, a spokesman for Mayor Mike Johnston of Denver, a Democrat. “It’s night and day. And we are seeing that when people do show up, it’s a little more akin to the normal patterns of migration.”

The number of buses sent by Texas has fluctuated, and there was period of about three months early in 2023 when there were no buses.

But the fact that, in the midst of a heated presidential race, no migrant buses have been sent to Democratic cities underscores how the steep drop in crossings has made it more difficult for Republicans, including former President Donald J. Trump, to maintain immigration and border security as a central campaign issue.

In July, for example, there were 7,200 migrant encounters recorded by Customs and Border Protection in the area that covers the border city of Eagle Pass, down from 71,000 in December. Across the entire southern border, there were 56,000 encounters last month, down from nearly 250,000 at their peak in December.

“It’s quiet,” said Valeria Wheeler, who operates a respite center in Eagle Pass and has worked with the state officials to identify migrants for the free, state-chartered buses, which are filled only with those who volunteer to take them.

Texas is still keeping buses stationed near the border, ready to carry migrants north, officials said. But the buses leave only if there are enough interested migrants. And there have not been.

What accounts for the dramatic falloff in migrant crossings since early this year continues to be debated. Mexican officials have taken steps to prevent migrants from massing along the U.S. border, in some cases transporting them deep into Mexico. Mr. Abbott has credited his increased deployment of razor wire and National Guard troops, as well as his takeover of a park in Eagle Pass in January, with driving migrants away from Texas to other border states.

Then Mr. Biden’s order dramatically curtailed crossings.

“Fewer illegal crossings into Texas means there are fewer buses departing for sanctuary cities,” a spokesman for the governor, Andrew Mahaleris, said in a statement.

Data obtained by The Times, from the start of the busing program through Aug. 4, showed that 28 buses left Texas in June carrying a total of more than 1,000 migrants. No buses left in July, according to the data. Texas officials said that so far no buses had left in August either.

Officials in El Paso, which had been the top origin city for the Texas buses, said only a small, manageable number of migrants were being released into the city on a given day — 27 on one day this week, for example. No buses were currently being organized there by the state.

“They’re still monitoring, we still monitor,” Mario D’Agostino, the deputy city manager for El Paso, said. “But there’s actually no demand for those charter buses.”