Why did Trump promise to use executive powers to put a hold on immigration from some countries?

Choices:
A. not enough information
B. these countries had too high of taxes
C. these countries harbored terrorists
D. these countries had pro-abortion rampant
these countries harbored terrorists
One day after a mass shooting killed 49 people at a gay nightclub in Orlando, Florida, presumptive Republican presidential nominee Donald Trump reiterated his support for a plan to temporarily ban Muslims from entering the United States.
At a campaign rally in New Hampshire Monday, Trump promised his supporters that, if elected, he would use the executive powers to "suspend immigration from areas of the world where there is a proven history of terrorism against the United States, Europe or our allies, until we fully understand how to end these threats."
Although the suspected Orlando shooter, Omar Mateen, was an American citizen, Trump suggested immigrants from the Middle East can come to the U.S. and radicalize people who are already here, or work to convince them online.
"The media talks about homegrown terrorism," Trump said. "But Islamic radicalism ... and the networks that nurture it are imports from overseas whether you like it or don't like it."
Refugees and immigrants from conflict ridden Middle Eastern countries like Syria, Iraq and Libya could "be a better, bigger more horrible version than the legendary Trojan horse ever was," Trump said.
But a recent Brookings Institution survey found Americans are far more welcoming of refugees than the billionaire candidate. Of those surveyed, 59 percent support accepting refugees, while 41 percent oppose it.
Those views are split right down party lines, with just 38 percent of Republicans supporting taking in refugees from Syria and the Middle East, compared to 77 percent of Democrats. But among Trump supporters, an overwhelming 77 percent said they oppose taking in refugees.
The Obama administration has set a goal of admitting as many as 10,000 Syrian refugees to the United States by the fall.Respondents of the surveys also were sharply divided on whether they would be willing to accept refugees from Syria in particular, with 61 percent of Republicans saying the U.S. should not accept Syrian refugees, compared to 27 percent of Democrats.
Trump supporters again overwhelmingly opposed accepting Syrian refugees, with 52 percent of them citing fear of terrorism as their biggest concern.