Transcript for Congress didn't specify 'what constitutes a [national] emergency': Terry Moran
You are looking live at the u.s./mexico border in Texas. A small portion of the nearly 2,000-mile stretch of land where president trump has declared a national emergency saying there is, quote, an invasion of our country. The president's plan is already being challenged on capitol hill and in the courts. It calls for about $6.5 billion from the Pentagon and treasury department budgets to fund the construction of trump's wall. A wall he promised Mexico would pay for. Trump is claiming the wall will guard against an invasion of drugs, but a recent assessment from the drug enforcement administration says the majority of heroin comes through legal ports of entry which would not be stopped by a wall. Then there is the president's claim that criminals and gang members are flooding across the border, but customs and border protection statistics tell a different story of the hundreds of thousands of people they have encountered. Only about 4% have been convicted of a crime and only about .1% of the undocumented immigrants are affiliated with gangs. Finally, there's the idea of an invasion itself. We have far more people trying to get into our country today than probably we have ever had before, and we have done an incredible job in stopping them, but it's a massive number of people. If we had the wall, it would be very easy. According to cbp, illegal immigration has actually declined dramatically over the last two decades. While there has been a recent surge of migrants from central America, it's made up mostly of families seeking asylum. Nine represent southern districts along the border. Eight Democrats and one Republican. None support the president's declaration. A growing number of Republicans are breaking rank. Senator Marco Rubio saying, no crisis justifies violating the constitution. Then there are the courts where trump is already facing legal challenges. So where do we go from here? For more on the two paths that could block the president's declaration, I'm joined by ABC's senior congressional correspondent Mary Bruce and senior national correspondent, Terry Moran who covers the supreme court. Welcome to both of you, and Mary, I want to start right away with you. Congress can try to pass this joint resolution to terminate the national emergency. How likely is the president to fare in that? How likely is that to get to his desk? Well, look. Democratic leaders have made very clear that they think this is a blatant power grab by they say, a disappointed president and Democrats will use everything they have to try to stop him. We have already seen the chairman of the house judiciary committee saying he wants to hold hearings and you have Democrats already planning to move ahead on that resolution to terminate and given how outraged Democrats are, it's very likely to pass in the house and it would put Republicans and the senate in a tricky position. There are numerous Republican senators who could join them. I have talked to many Republicans who said that they are -- that this is a mistake, that this sets a terrible precedent. You mentioned Marco Rubio. He says this is a violation of the constitution. The question is then even if it does pass through the house and the senate, what does the president do next? Because he can veto this, and chances that he gets two-thirds majority to override that veto, that's a high bar. What else could the Democrats do? They can shine a light on this decision. If the president ultimately can veto this, they're not going to be able to block that and pursue legal challenges and look at the courts and bring people up to the hill. Which brings us to Terry Moran and the courts. The president is sure to face lawsuits, already is, from legal groups. From states, from landowners. Let's take a listen here to what president trump said about that. We will have a national emergency and we will then be sued and they will sue us in the 9th circuit even though it shouldn't be there, and we will possibly get a bad ruling and then we'll get another bad ruling and then we'll end up in the supreme court and hopefully we'll get a fair shake and we'll win in the supret like the band. Very long list there, but he's gearing up for a long legal battle. Where are these lawsuits likely to focus? He has a nice wrap there and he knows the score because this is what's going to happen. How can I see you count the ways? That's what people are saying. The house of representatives controlled by Democrats. Say he's trying to S the power of the purse, but congress has delegated these powers to the president in laws that he's using. That's going to be a tough case. States, they have got a stronger case. This way this will impact their activities. Landowners. They will be displaced by eminent domain and that could be the sticking point. This is a long standing position held by the supreme our the government cannot exercise eminent domain without an express grant of power to do it by the congress. You might not be able to do it through an emergency declaration or an executive order, so you have real legal challenges coming ahead. There is something else he said in that Friday press conference that is getting a lot of attention. Let's listen to that. I can do the wall over a longer period of time. I didn't need to do this, but I would rather do it much faster. I didn't need to do this, but it's a national emergency? If you are the trump legal team, you just face palmed when you heard that. He is essentially undermining his own legal position. The position is this is a national emergency. I didn't need to do it. When congress and it granted this kind of power, did not specify at all what constitutes an emergency. So courts will have a hard time as they do normally second guessing the decision of a president on national security. Okay. Thanks very much to both of you.
This transcript has been automatically generated and may not be 100% accurate.