The Department of Homeland Security spent seven years and more than $1 billion trying to create a wall of technology at the border — or, as President George W. Bush called it, a “virtual fence.” It was a bust.

Now the idea has returned as the main ante for congressional Democrats in the border security spending fight. Opposed to President Trump’s physical barriers, they say drones, sensors and other electronics are all the tools needed — a “technological wall,” in the words of House Speaker Nancy Pelosi, California Democrat.

The Obama administration in 2011 pulled the plug on the Bush-era Secure Border Initiative Network, or SBINet, which was envisioned as an integrated system of radar, sensors and video cameras along the entire U.S.-Mexico border.

Democrats at the time cheered the decision to cancel the contract with Boeing for the long-troubled program.

Rep. Bennie G. Thompson, a Mississippi Democrat who was the ranking member of the House Homeland Security Committee, called SBINet a “grave and expensive disappointment” for squandering a little more than $1 billion to achieve just 53 miles of coverage on the border in Arizona.

Mr. Thompson, who now chairs the committee, said last week that he is ready to try again rather than spend on Mr. Trump’s corrugated steel fence.

“I have been engaging the tech community. They are telling me that they are developing modern technology that will help us identify those vulnerabilities. I would like for us to go in that direction,” he said on “PBS NewsHour.”

He said U.S. Customs and Border Protection already have high-tech sensors that just need to be used in a better way.

The Washington Times asked Mr. Thompson’s office what had changed since 2011 and whether he fully backed Mrs. Pelosi’s “technological wall.”

“He does support proven and effective technology to be used at the border where appropriate. SBINet simply did not work, was not deployed correctly and was overly ambitious,” said Thompson spokesman Adam Comis.

The border security debate and Mr. Trump’s demand for $5.7 billion for a border fence are at the heart of the standoff between the White House and Democrats that has kept the government partially shut down for more than three weeks.

Border security analysts agree that the technology has improved by leaps and bounds since 2011, but they disagree on whether sensors and remote imaging can substitute for physical barriers.

Jay F. Nunamaker Jr., director of the National Center for Border Security and Immigration at the University of Arizona, had no doubt that technology could replace walls and fences.

“The combination of all the cameras, night vision cameras, you could see people walking through marshes and streams like it was bright daylight,” he said, recalling a 2013 visit to a border security command center set up at Davis-Monthan Air Force Base in Tucson.

“Technology has only improved since then,” he said.

National security scholar James R. Phelps, co-author of the 2014 book “Border Security,” said the question isn’t whether the technology works in detecting border jumpers — it does.

“The question then becomes, ‘Do they actually stop anybody?’ The answer to that is no,” he said. “It is definitely not a substitute. It works in conjunction with physical barriers.”

A big difference between sensors and fences, he said, is where Border Patrol agents apprehend smugglers or illegal immigrants. The high-tech sensors and video cameras don’t prevent or hamper illegal border crossings.

“Once they are on U.S. soil, inside the United States of America, you now have to go through all the legal processes and administrative processes,” said Mr. Phelps. “You have to determine if they are here legally or illegally, collect the biometrics to put through the criminal check systems, detain them or arrest them, set them up for a deportation hearing, put them in front of a judge, potentially house them, treat them medically. The list goes on and on and on — with all the expenses associated with that person once they set foot in the United States.”

The scenario also depends on Border Patrol agents apprehending border jumpers after they appear on video screens.

“It does no good to detect illegal crossings unless someone is available to track them down, and fairly quickly, before the crossers disappear into the many private homes, farms, businesses, vehicles and natural hiding places that are in the border areas, often very close to the border,” said Jessica M. Vaughan, director of policy studies at the Center for Immigration Studies. “Technology by itself does not prevent anyone from crossing the way a real wall or fence does.”

Ms. Vaughan said the debate over technology versus walls is little more than a pretext for partisan posturing.

“The truth is, the Democrats don’t appear to want real border security, just to thwart Trump’s initiatives, which are what the career officials and the Border Patrol agents themselves are asking for — and they should know since they deal with this problem every day,” she said.

The abandoned SBINet project did help produce advanced radar, sensor and imaging equipment that the Border Patrol is using, although not as an integrated system across the entire 2,000-mile southern border.

As of October 2017, the most recent Government Accountability Office data available, Border Patrol had completed the planned deployment of select technologies to Arizona, Texas, California and New Mexico. The technology included remote video surveillance systems, mobile surveillance capability systems and 15 of 53 planned integrated fixed tower systems that use radar, cameras and night vision and correlate sensor information to provide a single operating picture.

However, the GAO reported that effectiveness of the high-tech gadgets in apprehending smugglers and illegal immigrants could not be assessed because of Border Patrol reporting errors.

In one case, Border Patrol stations in the Rio Grande Valley sector recorded assists from integrated fixed tower systems in about 500 operations from June through December 2016. However, the sector did not have the systems, according to a GAO report.