WASHINGTON — Washington used to know how to have a serious debate about border security.
Republicans demanded more money for Border Patrol agents and necessary fences. Democrats argued for better surveillance technology and more resources at the ports of entry. The two parties squabbled over how much to spend, how to pay for it and how it all fit into the broader struggle to overhaul the nation’s broken immigration system.
But President Trump has demolished the decades-old, bipartisan understanding about how to bargain over the border. In Mr. Trump’s world, there are no alternatives that can form the basis of a legislative give-and-take, much as his allies and adversaries might hope for them. For the president, the only way to stop what he calls an “onslaught” of illegal immigrants is to erect a massive, concrete or steel barrier across the nearly 2,000-mile border with Mexico.
“Drones and all of the rest are wonderful and lots of fun, but it is only a good old fashioned Wall that works!” he tweeted last month.
By conjuring images of a towering stone edifice around a medieval fortress — and branding those on the outside as invaders threatening to bring crime, drugs and disease to the United States — Mr. Trump has transformed what used to be a complicated, nuanced negotiation into a take-it-or-leave-it demand, laced with xenophobia, that has shuttered nearly a quarter of the government for weeks.
“He turns a debate that is fundamentally about more or less, measured in dollars, and makes it a debate that is wall or not,” said Frank Sharry, a pro-immigration activist who has battled over border security for decades in the nation’s capital. “It’s become cartoonish.”
For decades, immigration has been an emotional and bitterly fought battle in Washington and around the country. But even so, there has been a consensus among most Republicans and Democrats that securing the southern border requires a mix of costly strategies. That included a large number of Border Patrol agents posted at key points along the vast stretch of land from San Diego to Brownsville, Tex., fences in urban areas and barriers to stop vehicles from crossing and high-tech surveillance gear to alert the Border Agents to the presence of migrants and drugs.
Until Mr. Trump was elected, the sticking points had largely been about other parts of the broader immigration debate — cracking down on people who stay longer than their visas allow; preventing companies from hiring illegal immigrants; expanding opportunities for legal immigration; and providing status to those already in the country illegally, including immigrants brought to the United States as children.
Such a comprehensive deal is completely out of reach now. But Mr. Trump’s behavior during the past several weeks suggests that even reaching a smaller, more targeted agreement on security arrangements at the border is more elusive than ever before.
The current government shutdown, which began just before Christmas, is now the longest one ever in United States history. In the 22 days since the government shut down, there have been virtually no negotiations by congressional lawmakers or the White House. There have been no marathon, pizza-fueled sessions in back rooms at the Capitol. Lawmakers have not traded detailed proposals with each other. Mr. Trump refused to give an inch in his Oval Office speech, and has spent more time in an extended photo-op at the border than he has at the negotiating table.
It has all left veterans of past border debates exasperated and frustrated.
“We know how to secure borders,” said Alex Conant, a Republican strategist who was a top aide to Senator Marco Rubio in 2013 when the Republican senator from Florida helped lead the last major, bipartisan effort to overhaul immigration. “The 2013 immigration plan had what everybody agreed was the most effective way possible to secure borders and other points of entry.”
With the backing of President Barack Obama, a bipartisan group of eight senators that year succeeded in passing a comprehensive overhaul of the nation’s immigration system. But the legislation, which passed with 68 votes, prompted fierce opposition from conservative Republicans, who condemned it as amnesty for 11 million undocumented immigrants. It was never brought up for a vote in the House.
Still, the Senate legislation was an indication of where the two parties could agree on border security. It doubled the number of Border Patrol agents, from 19,000 to almost 40,000, an increase that even the authors of the proposal agreed was overkill but was designed mostly as an enticement to win Republican support.
Senators from both parties also agreed on money for technological improvements along the border. The bill allocated $3.2 billion for drones, infrared ground sensors and long-range thermal imaging cameras to give Border Patrol agents advance notice when migrants cross illegally, especially at night. It also included money for an electronic employment verification system for all employers and upgrades at airports to catch immigrants who overstay their visas.
And the consensus included some physical barriers — what Mr. Trump might call walls and others would call fencing. Years earlier, the Secure Fence Act of 2006 allocated money to build about 650 miles of barriers along the border. The 2013 bill, had it been signed into law, would have increased that total to almost 700 miles, mostly along the eastern half of the border with Mexico.
Almost all of the fencing that Congress has approved has already been built. In populated areas, the fence is tall and steel or chain-link and designed to keep people out. In other places, the barrier is nothing more than short, metal poles spaced out to keep vehicles from driving through, or low, wooden fences that run alongside pedestrian paths.
In 2011, a Government Accountability Office report concluded that despite 649 miles of completed fencing, the “the southwest border continues to be vulnerable to cross-border illegal activity, including the smuggling of humans and illegal narcotics.”
The report recognized that barriers have mostly not been built in the vast, empty stretches in Texas, where rivers and mountains as natural borders have prevented cars from crossing into the United States and made the trek by foot difficult, if not impossible. But Mr. Trump seizes on conclusions like the G.A.O. report’s about the continued influx of illegal immigrants at the southern border as proof that he is right in demanding a continuous wall.
In remarks to reporters after a meeting with Democrats at the White House earlier this month, Mr. Trump insisted that the only way to prevent immigrants from crossing between the 25 official ports of entry is to erect fences everywhere else.
“We can’t let gaps. Because if you have gaps, those people are going to turn their vehicles, or the gangs — they’re going to coming in through those gaps,” the president said. “And we cannot let that happen.”
But there continue to be questions about the wisdom of building a wall from “sea to shining sea,” even from inside Mr. Trump’s administration.
A different G.A.O. report, released last year, examined the preliminary cost estimates by Customs and Border Protection of what it would cost to extend the wall along the entire border. The report criticized the border agency, saying that the cost estimates did not take into account that costs would vary depending on the kind of terrain where they were built.
In recent days, the rhetoric between the two sides has become more strident than ever. Mr. Trump and his Republican allies have pointed out that Democrats supported fencing in the past, though they purposefully ignore the context of those votes and the difference between the fencing that Democrats supported and the all-or-nothing wall that the president has demanded.
Speaker Nancy Pelosi of California has called the wall “immoral,” cementing her position against it.
“At this point, the idea we could overlook the rhetoric and get a deal done is much harder,” Mr. Sharry, the pro-immigration activist, said.