Castro was among the last of a pack of 2020 candidates to speak at the South by Southwest Festival in Texas, in what amounted to one of the biggest gatherings of the Democratic field yet. As Democrats have addressed reparations in the early stages of the race, other candidates are discussing tax credits and other subsidies, rather than direct payments for the labor and legal oppression of slaves and their descendants. Vermont Sen. Bernie Sanders would put resources such as "Medicare for All" and tuition-free college into distressed communities.
Castro tells CNN's "State of the Union" he doesn't think that's the proper argument for reparations if "a big check needs to be written for a whole bunch of other stuff." Castro stopped short of saying he would push for direct compensation to descendants as president, saying instead that he would appoint a commissioner or task force that would make recommendations.
Sanders was in New Hampshire, while Sens. Elizabeth Warren of Massachusetts was in Dallas, Kamala Harris of California was in Miami and Amy Klobuchar of Minnesota was in Tampa. Other highlights from Sunday's campaigning:
The Vermont senator emphasized his rise from longshot candidate to major Democratic presidential contender in his first trip to New Hampshire since launching another run for president.
Sanders said his ideas that seemed "radical and extreme" four years ago are now helping define Democrats campaigns across the country.
"Those ideas that we talked about when I came here to New Hampshire four years ago, ideas that seemed so very radical at that time," Sanders said. "Well, today, virtually all of those ideas are supported by a majority of the American people and they are being supported by Democratic candidates from school board to president of the United States."
Sanders topped Hillary Clinton by 22 points in the state's 2016 primary. But he now faces a wider field of rivals who have adopted some of the same views on policy issues he pioneered during his last run for the White House.
"This is where the political revolution took off," Sanders said. "Thank you, New Hampshire."
Washington Gov. Jay Inslee laid down a challenge for his 2020 rivals — join him in calling to abolish the Senate filibuster.
Inslee is a newcomer to the Democratic field and is running a campaign that's almost singularly focused on climate change. But he was similarly adamant about doing away with the Senate filibuster while speaking to a small audience early Sunday morning at SXSW.
He said the six Democratic senators currently running for the White House shouldn't think twice.
"Maybe they get religion on this and realize that the filibuster is going to stop us from doing anything from health care to climate change," Inslee said. "As long as Mitch McConnell has the keys to the car, we're not going to drive it anywhere."
He was followed on stage by Castro, who also signaled an openness to the Senate doing away with the filibuster, which is a procedural tool that requires a supermajority of at least 60 votes to pass many big items, instead of a simple majority.
Former Colorado Gov. John Hickenlooper said he's not cut out for the Senate — and that he doesn't see himself switching races if his presidential run fizzles out.
"I don't see it in my future," Hickenlooper said.
Democrats have sights on Sen. Cory Gardner's seat. The Colorado Republican is up for re-election in 2020. Hickenlooper said he's spoken with Senate Minority Leader Chuck Schumer but says he considers running for president a calling.
Hickenlooper also said decriminalizing prostitution is worth exploring. He brought up the recent Florida crackdown on massage parlor prostitution and investigation into human trafficking, which resulted in New England Patriots owner Robert Kraft being charged with two misdemeanor counts of prostitution. Kraft has pleaded not guilty.
"There are a lot of arguments, and I think they're worth taking into serious consideration, that legalizing prostitution and regulating where there are norms and protections" to prevent abuse should be looked at, Hickenlooper said.
Democratic presidential hopeful Pete Buttigieg said Sunday night that he and Vice President Mike Pence have different views of their Christian faith and that he doesn't understand Pence's loyalty to President Donald Trump.
The mayor of South Bend, Indiana, said his feeling "is that the Scripture is about protecting the stranger, the prisoner, the poor person, and that idea of welcome. That's what I get in the Gospel when I'm in church." He said Pence's view "has a lot more to do with sexuality, a certain view of rectitude."
Buttigieg said he is puzzled by Pence's strong support for the president.
He asked how Pence "could allow himself to become the cheerleader of the porn star presidency?" and adds, "Is it that he stopped believing in Scripture, when he started believing in Donald Trump?"
Buttigieg made the comments at a CNN town hall in Austin, Texas.
Associated Press writer Hunter Woodall in Concord, New Hampshire, contributed to this report.
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