Transcript for Trump calls on Mexico to 'stop the caravans'

Thank you. Let's bring in Jon Karl for more on this, and Jon, all through the weekend talk of negotiations between the U.S. And Mexico to keep those migrants in Mexico, and now the president tweeting he may shut down the border permanently or at least try. Reporter: He is making that threat, but the administration is trying to work out a deal with the incoming president of Mexico. He takes office on Saturday. An agreement that would keep those migrants on the Mexican side of the border while they wait for those asylum claims. There are conflicting reports about the progress. The incoming Mexican interior minister said that no deal has been reached yet. Meanwhile the president is up this morning already tweeting about all of this saying that Mexico should send those migrants back to their home countries saying, do it by plane. Do it by bus. Do it any way you want, but they are not coming into the U.S. We will close the border permanently if need be. On the Mueller investigation, expected on Paul manafort, whether or not he is cooperating today. The white house appears to be bracing from a tough report from Mueller. I was talking to Alan Dershowitz who said it could be devastating. Reporter: It's a huge unknown here. The white house and the president's legal team, they don't know when this report is coming, in what form it is coming, but they are certainly bracing for bad news from Robert Mueller. The words from Alan Dershowitz who has been a strong supporter of the president were stark, saying this will be devastating to the president. Thank you very much.

This transcript has been automatically generated and may not be 100% accurate.