I would not say it is so much undermining support for immigration, as the media obfuscating the difference between Legal Immigration and Illegal Immigration.
There is the problem. "Migrants" just doesn't describe the millions of international party crashers who have invaded our country, uninvited, without so much as a 'by your leave', but for all practical purposes, at the behest of an administration that has done everything but send them a plane ticket here (and, who knows, may even have done that).
"Immigrants", whether or not you were a fan of their native culture or individual personalities, once were people who had filled out the paperwork, who, in earnest, came here to become American. Then we hyphenated them, and balkanized their individual cultures into various ghettoes, and only the most intrepid walked out into the great world of opportunity that was America, to work hard, and become the best them they could be, fully embracing their new country.
Illegals, on the other hand, are here to exploit, whether benignly or malignantly, our economy and way of life, here without invitation nor permission, undocumented, and not here to become Americans, but to get what they can before they get sent home, although that is a hollow threat at present.
I'm not against immigration, at least that which is composed of people who genuinely want to become Americans, who will revere a shared culture in the Constitution and our (productive) way of life.
But those who come here and whose first act (entering the country illegally) shows a contempt for our laws, a fundamental disdain for our way of life, I'd just as soon leave on the other side of the border. Others, who have for all practical purposes been accessories to those crimes can go, too--regardless of what office they may hold or have held.