Building a border wall will likely involve taking private land, potentially a lot of land. When the landowners don’t want to sell, the government can invoke eminent domain.
The following site provides background of what happened in one such famous case of Kelo vs. New London. The outcome of that case also strengthened a backlash and potentially eminent domain laws in the US.
These delays and now rescheduling might have an effect in both direction. An asylum seeker, perhaps with a not very strong case, might stay even longer in the US before a judge denies an asylum request. An asylum seeker with a strong case might have have that case become less strong, e.g. if they were providing for a sick dependent who then dies.
One of the selling stories for a wall has been personal anecdotes and stories about crimes committed by immigrants. Those anecdotes may not be backed by actual statistics.
Approximately 3% of the US population are undocumented immigrants. There are approximately 20,000 homicides per year. So statistically it would make sense if there were 600 homicides by undocumented immigrants per year. I don’t think precise statistics are kept each year but studies at least suggest the rate of violent crime is lower on average.
So why didn’t the GOP take care of this business and decide to build a wall when they controlled both houses of congress?
The answer seems to be that while it was the top issue for a minority of legislators, it was never the most important issue for most legislators.
The first clue comes by looking at statements from Texas legislators just before they took office in 2017, there was not a single one on record supporting a wall across the entire southern border, despite 79% voters saying they were in favor.
Some Republicans as Pete Sessions described the wall as “an analogy”, many others made statements for “border security” while being careful to point out that a wall wasn’t the only solution. Some Republicans just didn’t answer.
Democrats were more uniform in their responses in being opposed to a wall across the entire border, while sometimes also making statements in favor of border security.
So when it came time to put up the legislative priorities in 2017, building a wall took a back seat to repealing Obamacare and to Tax Reform. Republicans were unwilling to spend the political capital necessary (e.g. using the reconciliation process if necessary in the Senate) and were willing to trade off a border wall for other priorities.
The border wall must cover the entirety of the southern border and must be sufficient to stop both vehicular and pedestrian traffic.
Neither of those is particularly realistic. Perhaps the best way to see this is to read accounts from those who know the border best.
The following site is a web site from two women who recently hiked from San Diego to the Gulf of Mexico following the US/Mexico border. It isn’t explicitly political but does provide a good perspective on state of the current border and the variety in both the border and the existing fences.