Transcript for Trump to argue for border wall in primetime address

And we'll get to it all. We're going to begin with the president, delivering his first ever primetime address in the oval as. The president asking for national airtime to make his case. Why he says the U.S. Needs to build a border wall. A promise he made often on the campaign trail. He also promised Mexico would pay for it. Now, it would be U.S. Taxpayers. And all of this paralyzing government. Day 18 now of the shutdown. Jonathan Karl leading us off tonight with what we've just learned. Will the president declare a national emergency to get the wall built? Reporter: Tonight, president trump makes his case to the nation, selling his border wall with a primetime address. His first from the oval office, as the government shutdown take as toll. This shutdown could end tomorrow. And it cold also go on for a long time. Reporter: 800,000 federal workers are not being paid. Farmers aren't getting their government subsidies. Pilots are warning about airline security as TSA officers work without paychecks. Christine vitel, a single mother, works for the TSA at Chicago o'hare. I live 39 miles away from the airport. That's one way. My gas is what takes up my money. I can go probably one more pay period without getting paid, but most people can't go one more day. Reporter: The president says he understands what workers are going through. I can relate. And I'm sure that the people that are on the receiving end will make adjustments. Reporter: He has made his case with a blizzard of false claims. And today, I asked vice president Mike pence about the administration's credibility under fire. How can the president be -- how can his word be trusted on this when he has said so many things that are just not true about this crisis? He said that Barack Obama has a ten-foot wall built around his house here in Washington. You know that's not true. He said that some of his predecessors told him that they wanted to build a wall. But all four living presidents have now put out statements saying they never had any such conversation with the president. And then you saw Sarah Sanders say that early 4,000 terrorists come into the country every year and, you know that's not true, either. How can the American people trust the president when he says this is a crisis when he says things over and over again that aren't true? Well, look, the American people aren't as concerned about the political debate as they are concerned about what's really happening at the border. And that's what -- Reporter: They're questioning his credibility. The white house said nearly 4,000 terrorists are coming to our country. That's not true. Jon, nearly 4,000 known or suspected terrorists were apprehended attempting to come into the United States through various means last year. Reporter: Overwhelmingly at airports, not at the border. And Jon Karl is with us at the white house. The address just hours away, and the president has not made a crucial decision before his speech if. Reporter: I just spoke to a senior white house official said the president is still making changes to that speech, and he has not decided whether or not to declare a national emergency and thereby try to go around congress. No decision even now made on that. As for the Democrats, they are already slamming this speech, predicting it will be filled with, quote, malice and misinformation. They also have the demanded time from the networks, and David, they will get it. All right, Jon Karl, we'll

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