The main reason why they don't want the wall

There main reason why some in congress want these illegals here is self preservation. These Illegals will vote illegally for them (as they did in Orange country in 2018) but they also increase the population in democratic strongholds which gives them more representation in congress in the House.
Trump is demanding that in the next census you must declare if you are a citizen as you should. Democrats are of course fighting this as it works in their favor.

• No citizenship on census = more illegal voters and more dems in the house which is based on population - needs to be based on population of citizens
• No border wall = more of the above plus these are the people dems need to infiltrate other red states. They are willing to move so these law breakers can be pushed into other states to change the voting demographic and crush the electoral college. 
• Sanctuary cities give illegals a place to hide and vote and increase House rep calculations
• Dems want to remove the electoral college because their waves of invader illegals will give them a majority just as they did in 2016 in California.
• Illegals = big kick backs from UN and Soros groups aiding migrants and pushing welfare
• Illegals provide cheap labor which allows congress to extort big business for donations and jobs for their families from the businesses who get to pay illegals much less and increase their profits.

The solutions are simple:

1. Identify citizens on a census now so we know how many voters there are
2. Setup a voter ID to ensure only these citizens are voting
3. Eliminate sanctuary cities to eliminate the staging areas for illegal votes and census
4. Build the wall to stop democrats &  illegals tampering tampering with our elections
5. Stop aid to UN foreign aid groups who create the migrant caravans and payoff politicians

The other issue with illegals is of course the theft of millions in taxes which I pointed out here.  Democrats have to pay these illegals back for keeping them in office and they do that by giving them welfare and education and free medical while you get nothing and your taxes actually pay the welfare.

It's all about the kickbacks and of course any mafia extortion type organization like our congress has to have enforcers and that is the function of MS13 .... as maybe Seth Rich could tell us. I'm sure you were astounded to hear Pelosi call them children as we all were when their numerous crimes are so well documented. They provide punishment for any dissenters and how much easier is it for them to do so against a population that has no weapons to defend themselves in Democratic run cities. This is nothing new to the democrats or as they should be called now the communist party of america ... they've been doing this since the 1900's.

It very well may have been these type tactics in the 1930s that gave us WWIII