At the Pentagon Thursday, President Trump addressed the deaths of the four Americans killed in a targeted attack by ISIS in northern Syria on Wednesday, expressing his "deepest condolences to the families of the great American heroes who laid down their lives yesterday," and calling them "great, great people."

Last month, Mr. Trump declared victory in the battle against ISIS in Syria. The president's speech then very quickly segued to talk about the need for a wall at the southern border. He said that more caravans are already forming and said the government is still shut down because Democrats refuse to fund border security.

"The party has been hijacked by the open-borders fringe," he said.

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The president also addressed NATO, an entity he has criticized some in the past.

"We will be with NATO 100 percent, but as I told the countries, you have to step up and you have to pay," Mr. Trump told his audience at the Pentagon.

The president was at the Pentagon as his administration rolls out its plan to ramp up missile defense capabilities in response to threats that may be posed by potential adversaries. The administration's strategy will possibly entail a new layer of spaced-based sensors to spot enemy missiles.

"Our nation does not seek adversaries, but we do not ignore them, either," Acting Defense Secretary Patrick Shanahan said Thursday, noting that a missile defense strategy requires offense.

Space is key to that missile defense strategy, Shanahan said Thursday, in an announcement that comes as Mr. Trump is working on plans for a "Space Force" as the sixth branch of the military.

The Trump administration recently completed its review of what it is describing as the United States' first "major" and "comprehensive" review of the United States' missile defense policies and capabilities since 2010. One senior administration official explained to reporters in a conference call Wednesday that a "significant change to the threat environment" has been seen in recent years.

"What the missile defense review responds to is an environment which our potential adversaries have been rapidly developing and fielding, a much more expanded range of new advance offensive missiles," the senior administration told reporters. "Some of these missiles are capable of threatening the United States, threatening our allies, our partners."

Senior administration officials shared little on exactly the threats the U.S. is concerned about, but one senior administration official said the United States' missile defense capabilities "are primarily postured to stay ahead of rogue states' threats."

Last year after meeting with North Korean leader Kim Jong Un, Mr. Trump declared North Korea to no longer be a threat. Senior administration officials, asked whether there is still a threat from North Korea, deflected.

"The review does look at the comprehensive environment that the U.S. faces, that our allies and partners face, and it does posture our forces to be prepared for the capabilities that currently are a threat and that we anticipate in the future," a senior administration official said.

— CBS News' Fin Gomez contributed to this report