That's because strict closed border policies are widely supported across both sides of the political aisle, with the exception of some elites. Organic sentiment even on the Left will always strongly favor it because it's protectionist and pro-union.
Interesting story my uncle told me about an acquaintance of his, guy that owned a construction company. He'd go round up a bunch of illegals and offer them work. Deal was that they'd stay in a house he owned, eat the food he provided (cans of beans and packages of tortillas basically), and once the job was completed he'd pay them out of the money from that. So these guys would put in weeks of construction work and, when the job was just almost completed, this guy would call immigration on them and get them deported. He'd bring in another crew, pay them for like two days of work max, and then start the whole process over again. Sometimes he'd even pick up the same guys. "Hey, you know what the arrangement was, and you didn't finish the job. Don't worry, you'll get paid this time." Effectively everyone gets shafted... the illegals get shafted out of everything but basic room and board for two months, the professionals only get paid for two days instead of two months.
Now, one person hears that and their thought is "Maybe if we stopped illegal immigration, guys like that would have to give up their shitty schemes and actually pay their legal workers a decent wage."
Another person hears that and thinks "That's terrible! He shouldn't be able to treat his slaves like that! We should get rid of the immigration authorities!"
Immigration control & enforcement (when you strip out the buzz words the lugenpresse has contitioned the lefties to froth about) has wide-spread support accross the board from normal employed citizens.
Where it doesn't have support is from any labor-intensive business owners, of the sort
@Jigglyjogglers mentions, because of the money to made exploiting people outside of the system. Even if the fellow JJ's example paid his day laborers, it'd be nothing compared to what it'd cost him to try to hire citizens or legal immigrants.
Which creates a self-perpetuating problem. Switzerland allows a fairly staggering number of work visas for low-skilled labor, because they need it. The US needs it too. But because the illegal market is undermining the legal market, there seems to be no need for low-skill legal labor. If you allowed more low-skill legal labor to enter, you will be having them compete against citizens for what seems like not enough jobs. There are more than enough jobs, they are just being filled with illegals. If you actually well and truly shut off the illegal labor market (and made it clear the good old days weren't coming back), you would see so many fast-tracked (and needed) reforms to US immigration come so fast because the US economy needs (temporary) access to low-skill labor.
Trump just tightening the screws a little bit and spreading a bit of fear in the wetback population has caused fastfood places in high-cost areas to actually start offering wages in excess of the much-a-blooed about $15/hr, because sanctuary or not, the Illegals aren't hanging around and now you actually have to hire people for W-2 wages you can't pay under the table.
If you shut off illegal immigration, companies can't abuse their "vulnerable" workers any more. They can't skate on payroll & local taxes anymore. The money they make has a better chance of staying in the community.
I want to add in something about my conflicted feelings about the US brain-draining the rest of the planet, but this is a long and gay enough post.
FDR through JFK. And for a couple of weeks in the Carter administration.
Hell no. They were just being quiet about it. I'd say the only D in the past 250 years who wasn't actively advancing the Democrat plantation life in one way or another was....maybe Truman?
JFK & LBJ did everything they could to deepen black's dependence on the state & government benefits.
Need I remind you that most of her consitutients believe AoC is a genius-level intellect, is doing a great job, and isn't far enough left?