McALLEN, Texas—The Department of Homeland Security denied Cameron County’s proposal to build miles of combined border wall and levee along the border’s southernmost point.

In a letter, U.S. Customs and Border Protection Commissioner Ralph Basham told Cameron County Judge Carlos Cascos that they had determined the project “is not feasible.”

Basham cited the cost of the project based on similar work in neighboring Hidalgo County and inability to coordinate the work with the International Boundary and Water Commission, which has already started building up the county’s levees.

But Cascos said he believed the driving force was the congressionally-mandated deadline to build 670 miles of pedestrian and vehicle fencing along the U.S.-Mexico border by year’s end.

“I think this could have been done,” Cascos said. “I think DHS was concerned about the deadline.” Cascos said he had heard earlier that the county’s proposal would not fly, but did not see it in writing until Tuesday.

On Monday, when asked about the project’s timeline, Cascos had said, “If we don’t get started last week, we may not be able to meet the deadline.”

With just more than four months remaining in the year, no border fence construction has started in Cameron County.

Several land condemnation cases remain in court and earlier this month received trial dates for next year. U.S. District Judge Andrew Hanen indicated he could give the government access to the parcels as early as September so the project could proceed while compensation for landowners is worked out in court.

A compromise Hanen approved between Homeland Security and the University of Texas at Brownsville about border fencing on campus appeared to clear the way for that once hotly-contested segment to become the first to get underway in the county. The university received government approval for its fence design and requested proposals last week.

The Army Corps of Engineers invited contractors to bid on three of the Cameron County fence segments—of a total 35 miles planned for the county—in May, but none have been awarded.

Three of the contractors who initially expressed interest in the work said Monday the contracts were on hold but they were unclear why. One, who did not want to be identified because the project details are classified as confidential, said the talk among contractors is that the government is waiting to see which candidate wins the presidential election.

Katherine Shelton, an Army Corps of Engineers spokeswoman in Fort Worth did not explain the delay, but in reference to the end-of-year goal, said “that’s the drop dead deadline.”

In Hidalgo County where construction has been underway since July on two fence segments, there has been talk of flexibility in the deadline.

Godfrey Garza, head of Hidalgo County Drainage District 1, which is overseeing the county’s part of the project, said Monday that Homeland Security had recently offered the county some extra time to complete the work. The county’s initial agreement with Homeland Security had already allowed some finishing touches to be completed past the end of the year. Still, he said the project was on schedule.