Transcript for 'I don't think [Trump] knows how to act' in office: Possible 2020 GOP challenger Weld

I have established a committee to pursue the possibility of my running for the presidency of the united States as a Republican in the 2020 election. I encourage those of you who are watching the current administration nervously, but saying nothing to stand up and speak out when lines are crossed in dangerous ways. We cannot sit passively as our precious democracy slips quietly into darkness. That's former Republican governor of Massachusetts and 2016 libertarian party vice presidential candidate, bill weld. He's the first Republican to consider a primary challenge to the president and he joins us now. Welcome. Thank you for having me, Martha. It's been a long time since I covered your governor's race back there in Massachusetts. Now you're exploring a run for president as a Republican. Our latest ABC news/ "Washington post" poll, showed the president maintains a 78% approval rating among Republicans. The Republican national committee passed a pledge to give president trump its undivided support. What is your path forward here? Can you really get the support needed for this serious challenge? I think the Republicans in Washington want to have no election basically. I don't think that would be very good for the country and I have a lot of views of how the president is acting in office, you know, I don't think he knows how to act. He thinks he has to humiliate whoever he's dealing with or else he's half a man. The emergency declaration is just one example of that. Congress thought they had a deal. He says, oh, you think you have a deal? I'm going to show you a deal. I'm going to show you who's boss. It's no way to run a railroad. What is your path forward? Well, I'm going to make clear that I think the president is reckless in spending. They're spending a trillion dollars a year. They don't have that. It's going to crush generation x-ers and millennials in this country. They are not thinking ahead. 25% of the jobs in the country are about to disappear because of artificial intelligence and robotics and drones and machine learning and autonomous vehicles. Nobody is planning ahead of that, and it would entail a lot of work to make sure that the people who lose those jobs get the skill sets to get their replacement jobs when they show up around the same time. If we play that right with our educational system, the people that lose their jobs could wind up with higher wages than they had before. If we don't do anything, then the door to the middle class is going to be shut on the working poor which would be very bad for the country as a whole. That's the sort of thing they're not paying attention to in Washington because they're so busy with divisiveness and trying to make everyone feel awful. Your former press secretary told "The Boston globe," if the goal is defeating trump, the best option is to run as Republican because primary challengers -- he means you, have historically weakened sitting presidents. So is it your ultimate goal to weaken president trump for the general election rather than beating him in a primary? Not rather than beating him, but it is part of my thinking to make sure he doesn't repeat. We don't have six more years of the antics frankly for wont of a better word that we have seen the last two years. I think that would be bad for the country and I don't care who knows it. You know, we talk about Republican support and approval among Republicans, but what do you say to the hard core trump supporters who think he has done a great job on national security, on the economy? Likely on the wall. What's the case you will make? Done a great job on the wall. He has flung it about. Let's talk about his supporters, his base of supporters. What do you say to them? I would say his whole hyperemphasis on the wall is pure politics on his part and it's vintage what he has done since he entered this race. He wants to divide the country and hold upu know, scary boogeyman that everyone else can think, only he can save us. It's part of a plan I think on his part to make himself seem indispensable. He's not indispensable at all. People, you know, getting through between the fences that are already on the border with Mexico are not a national emergency, and they're not a major nationalurity threat to the United States, and I think everyone who studies the situation knows that, but it's pure rhetoric on his part without anything behind it. The GOP chair from your home state of Massachusetts issued this statement after you announced noting some of your past dances and of course, you're a libertarian before and said you would be for life and now you're a Republican. Weld is the same ex-republican who deserted Massachusetts for New York who endorsed Barack Obama over senator McCain for president, who renounced the GOP for the libertarian party, while running against pence/trump Republican ticket, while cozying up to Hillary Clinton. Even Benedict Arnold switched allegiances less often. How do you convince that Republican base? I know what you are trying to do this morning, but they see that record think you're not for the Republican party. I'm not going to convince the Republican state chair. They're under pressure. Make sure this guy gets no purchase and make sure we don't have a primary. We want to sail through this without having to think or analyze issues and I think it's not what the country needs to put it mildly. You have a lot of work ahead of you, governor. It's great to see you always. Thank you.

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