The fence was never completed but your insane support for all things left leaves you blinded and unable to see anything that does align with your supposed facts, the problem I see with fanatical Democrats like yourself is that you only see what you believe even if its really dumb.
I haven't heard Schumer say why he changed his mind, but it might be that the portion of fence/wall that was completed has created a lot of problems and pretty much solved nothing. Drug cartels tunneled under the wall in several places and illegal immigrants either go around or over. Most of the people coming across the border today are people seeking asylum and all they need to do is get onto US soil. The wall needs to be built within the US border so all they need to do is get to the Mexico side of the wall and they will be in the US. A lot of drug traffic also comes into the US on trucks carrying other commerce.
Security experts have pointed out that a virtual fence is far more effective at catching anyone trying to get through the border and either smuggle drugs or illegally immigrate will get caught in a net of motion and vibration sensors monitored from a central location with response teams to turn up if anything interesting happens.
Building a wall or fence is a 5th century solution to a 21st century problem. It's throwing money away on a symbolic, but pointless gesture. A wall made of garden gnomes lined up shoulder to shoulder would be just as effective and probably cheaper.
American politics, vetter than Brexit I guess.
The way I see it from the outside looking in....
Regardless of policies or people resisting trump just because it's trump, your government equivalent are realising if they give in to demands even from a president ( who appears to demand his own way, which is not a bad thing to have a strong leader) where does the giving in to demands stop, if Trump wants a pony or better yet a unicorn he will just shut down congress untill some one makes one appear.
I was under the impression the government dose not negotiate when backed in to a corner ( not going to use the word terrorist as its not the correct use but would reiterate a point).
On the same side of the coin if a child misbehave and you let them have there own way you are making a rod for your own back!!
On a less bias biew, I only wish Mrs May had some of the bollocks Trump had, as this EU thing would be done and dusted!
I follow UK politics relatively closely, though not as close as US politics. The positions of the US Republican party are very close to the DUP. The only difference is the DUP have 8 seats in Parliament and the Republicans run the country.
The Republicans consider taking a position and refusing to budge a good thing, even when it turns out the idea is unworkable or just plain stupid. They criticize Democrats for being willing to negotiate and/or change their minds and call it a weakness. Most sane people consider those to be honorable or at least reasonable traits.
Though when I hear the Brits complain about their politicians like Boris Johnson or Jacob Rees-Mogg I want to offer to trade. By any reasonable measure the UK is poorly led right now and there are some very poor politicians in leadership (or recently resigned), but all of them run circles around Donald Trump in both the competency and honesty department.
The Democrats in recent years have been decent at governing, but poor at politics. The Republicans have weaponized politics but completely forgot how to govern. The new generation of Democrats are learning how to play politics again and may be at least as good at governing as the older generation of Democrats (most are still too green to tell yet).