President Donald Trump has announced a dramatic shift in his immigration policy — something White House adviser Stephen Miller has reportedly been pushing for behind the scenes.

The move follows the shooting of two National Guard members in Washington D.C. Wednesday and is part of a long-term strategy for Miller, who has long voiced he wanted a more aggressive approach to immigration and increased deportations, Tamara Keith, NPR White House Correspondent, said on CNN Friday.

"This is very much in line with the way that the president and people in his administration, people like Stephen Miller, have been talking about immigration. President Trump in his remarks on Wednesday night brought up Somalia. That is not an accident. That is something that the president has been focused on recently and that he is emphasizing," Keith said.

"You look at refugee policies where the White House wants to bring in white people from South Africa, who they say are being persecuted. They don't want to bring in other refugees. The refugee program has been severely restricted under the Trump administration already," Keith added.

As Trump's approval rating has sunk, his administration has shifted their attention to immigration.

"In a lot of ways, this is a terrible event that has given them a sort of a peg, to do the things they were already doing or wanted to do," Keith said. "And it does come at a time when the president's approval rating is in a really bad place, including on immigration, but this is a realm of immigration that he has had more traction than some of the other areas."

Trump on Thursday made the announcement that he had ordered U.S. Customs and Immigration Enforcement to review every Green Card holder “from every country of concern,” a list of 19 countries his administration named in June.

Those 19 countries include Afghanistan, Burma, Chad, Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, Yemen, Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela.