Unless those illegals become naturalized, they can't vote legally. I don't know if naturalized citizens who can vote favor Democrats or Republicans. But I've met people from El Salvador or South America who lean Republican but I've also met West Indians and African people who are clearly Democratic voters.
Your friend should have gotten a job here. But immigrants, much like native workers, exist in the two dimensions of workers of highly educated and those who are not. Even the uneducated contribute to the economy. Most of these immigrants do jobs Americans are too cool for. There is a poultry processing plant twenty minutes away from my home. It's hard to see anything but Hispanic people coming in and out. The same thing is present in agriculture too. Around 2010 during the recession, Alabama and Georgia passed bills making it harder for illegals to work on farms and both states suffered losses due to labor shortages. Interestingly, this same phenomenon happened and is happening in the UK now. Due to Brexit, the Polish immigrants who make up a significant amount of agricultural workers are now leaving the agricultural sector in a bind. I've bought gym guest passes from different gyms all over the country. Save for one gym in Colorado Springs where the cleaning staff was white, nearly every gym I've visited including those in my state are cleaned mostly by Hispanic people. The cleaning crew at Target and Walmart? Same thing.
It's important to remember this administration wants to limit all immigration, including people like your friend. Bannon and Miller hate that H1B visas are going to so many immigrants (which is what your friend was likely eligible for, unless he was sponsored for a green card by a US relative or married an American. Either way, both paths would have solved his legal status issues).
It's easy to argue limits on immigration would affect people like your friend more because he's playing by the rules. Illegal immigrants don't play by the rules. If you want to limit illegal immigration, remove the incentives for employers that benefit from cheap labor by investigating them. But be careful what you wish for, because when employers pay fair wages in agriculture and services they will pass that cost onto consumers.
