Trump has tweeted about chain migration:

CHAIN MIGRATION cannot be allowed to be part of any legislation on Immigration!

— Donald J. Trump (@realDonaldTrump) September 15, 2017

Yahoo News, where like most MSM outlets, they've never heard of chain migration,interviewed some major Treason Lobby figures—note the adorable children in the background of their graphics, as well as two Statues of Liberty:

Heidi Beirich, the director of the South Poverty Law Center’s (SPLC) Intelligence Project, told Yahoo News that “chain migration” is a phrase “from the anti-immigrant world.”

And Ms. Beirich is speaking from the pro-immigrant world.

It is popular among groups that want to reduce legal immigration levels like the Federation for American Immigration Reform (FAIR), the Center for Immigration Studies (CIS) and NumbersUSA.

“They don’t like it because they argue that it brought all these kinds of ‘undesirables’ to the United States,” Beirich said.

Trump’s sudden declaration Friday could be of some comfort to immigration hardliners wary of his recent outreach to Democrats and young people protected by the Deferred Action for Childhood Arrivals (DACA) program.

Democratic leaders Sen. Chuck Schumer and Rep. Nancy Pelosi shocked Republicans Wednesday night when they announced that he had agreed not to deport the roughly 800,000 undocumented immigrants who had been shielded by DACA.[Trump abruptly attacks 'chain migration,' a term that worries immigration advocates, by Michael Walsh, Yahoo News, September 15, 2017]

As Breitbart points out, stopping chain migration is likely to kill any deal with Democrats—it's a major part of the whole "Electing a New People" thing.

Democrats, however, strongly oppose any curbs on chain-migration because they are relying on a huge inflow of unskilled immigrants to win national political dominance. Without the new chain migrants, the Democrats’ progressive leaders would be forced to humiliate themselves by offering pro-American concessions to American voters.

For example, the emerging deal between Trump and Schumer would provide quick citizenship for at least 3 million illegals via the “Dream Act.” But those 3 million could bring another several million immigrants — and likely Democratic voters — via “chain migration” during the following ten years.

If you replace DACA with the DREAM Act, that will be 3 million plus. After chain migration it will be the biggest amnesty in modern history. https://t.co/rlS9035qJO

— Federation for American Immigration Reform (@FAIRImmigration) September 14, 2017

Most media coverage of the DACA deal suggests it only covers the 700,000 “dreamer” illegal immigrants who are now protected by former President Barack Obama’s 2012 “DACA” amnesty. Schumer and House Minority Leader Nancy Pelosi insist that the deal endorses the much larger Dream Act, which would ensure a much larger wave of subsequent chain migration.

Business groups fully support chain migration because it imports an roughly 400,000 new welfare-funded customers and potential cheap employees each year.

Donald Trump: End Chain Migration, Neil Munro, Breitbart, September 15, 2017

Read the whole thing at Breitbart—Neil Munro knows what he's talking about, or if you don't have time, just give thanks for a President who has even heard of chain migration.