"I'm all for speaking with adversaries but what's happened here is the president has raised the profile of a dictator," the former Housing and Urban Development secretary told ABC News Chief Anchor George Stephanopoulos on "This Week," adding that the meeting was "all for show."
"I think that he should put the work in beforehand and hold him accountable to a commitment that he made in the Singapore summit," Castro said. "I don't think that it's fitting for the United States to continue to radically meet with a dictator when they haven't abided by the first terms a year ago."
The interview on Sunday follows Castro's breakout performance on the first night of the Democratic presidential debate on Wednesday, which spawned his strongest day of fundraising, according to Castro's campaign. On Thursday, the campaign announced it raised 3,266% more money than it had in the previous two days.
Castro has carved a lane for himself on immigration reform, even as some of his proposals have been criticized as being in favor of "open borders." On the second night of the debate, candidates were asked, by a show of hands, if each of the 10 candidates on the stage would provide health care to undocumented immigrants. All of them raised their hand. Asked by Stephanopoulos if he supported that effort, Castro said he did.
"Number one, undocumented immigrants already pay a lot of taxes. Secondly, we already pay for the health care of undocumented immigrants, it's called the emergency room," Castro told Stephanopoulos on Sunday. "And then third, it is the right thing to do. We're not going to let people living in this country die because they can't see a doctor. That's not what we are as Americans."
While there is wide consensus among the Democratic field that everyone should have access to health care, ideas on how that should be achieved vary. The discussion of providing Medicare for all dominated both nights of the debate. Even though Castro was not on the stage with Sen. Bernie Sanders on the second night, he said he agrees with him that "everyone who wants Medicare should have it." However, he disagrees with the Vermont senator's proposal to abolish private insurance.
"I also agree with Sen. Sanders when he says, and many people have pointed out that, you know, there's a lot of profit that goes into these insurance companies into 'big pharma', and we need to put more of those resources into actually providing care for Americans," he told Stephanopoulos. "I think that people can hold on to some sort of private supplemental plan if they want, that there's no reason that we shouldn't allow them to do that."
During the interview, Castro called his vision for immigration reform a "more humane and smarter" way to deal with border security and immigration in contrast to that of Trump and the Republican Party.
"This president has wasted two and a half years, he knew what we had a flow of people that were coming from Central America, when he became president on Jan. 20 2017," he said. "He's wasted two and a half years because he should have done what I've called for, which is a 21st century Marshall Plan with those northern triangle countries, so that people can find safety and opportunity at home, instead of having to come to the United States."
His immigration proposal also calls for an increase in refugee intake, something the Trump administration has decreased.
"Right now, we're only taking in between 30 and 40,000 refugees, I would like to see that go up to the statutory limit," he said. "And we're big enough to do that. There have been times in our history in this country where we're taking in a lot more people and we became a stronger nation for it. What's underlying this and what the president likes to count on, is the fear and the paranoia that he's stoking."
On Wednesday night, one of the most heated moments on the stage came during a fiery exchange between Castro and fellow Texan and former congressman Beto O'Rourke over decriminalizing border crossings, one of Castro's signature immigration reform proposals.
Castro wants to repeal Section 1325 of the Immigration and Nationality Act, which makes border crossings a criminal offense.
As O'Rourke was laying out his proposal to prevent family separation during the debate, Castro spoke over him saying, "Your policies would criminalize a lot of these families." Castro then accused O'Rourke of not doing his "homework" on the subject.
"I just think it's a mistake, Beto, I think it's a mistake." Castro said. "And I think that if you truly want to change the system, then we've got to repeal that section. If not, it might as well be the same policy."
Castro's proposal to decriminalize border crossings from a criminal offense to a civil one, has become somewhat of a litmus test for presidential candidates as President Donald Trump's family separation policies come into focus.
"There's no way that we can call that open borders because we have 654 miles of fencing, we have thousands of personnel at the border, we have planes, we have helicopters, boats, security, cameras, guns," Castro said. "That's by no stretch of the imagination, open borders. And then, you know, secondly, there is still a civil court process. There are still people who are being deported. There are people applying for asylum that do not receive or not granted asylum."
Castro has struggled to gain traction in the polls since announcing his run for the White House in January. In May, he told reporters that people were "sleeping" on his campaign, lamenting that his name recognition wasn't as high as some of the Democratic frontrunners.
Shortly after the debate, Castro told ABC News that he was confident that had all changed because of his performance.
"They see that I have the right experience to be president," Castro said. "I can handle myself, you saw that tonight and I can beat Donald Trump."