On the second night of the Democratic presidential debate in Miami, NBC moderators asked candidates whether they would support decriminalizing the act of illegally crossing the border into the United States — that is, reducing the seriousness and consequences of illegal entry to the level of a parking ticket.

"Raise your hand if you think it should be a civil offense, rather than a crime, to cross the border without documentation," said NBC's José Díaz-Balart.

All 10 candidates — Biden, Sanders, Buttigieg, Harris, Gillibrand, Bennet, Swalwell, Hickenlooper, Yang, Williamson — raised their hands in approval. That moment was perhaps the Democratic Party's most significant step yet toward embracing a policy of open borders.

The show of hands followed a similar discussion the night before, in the first debate with another 10 candidates. The question was not asked of all of them, but lower-tier candidate Julián Castro stole the show by advocating the decriminalization of all migrant crossings — he originally proposed the idea in May — and going into detail about the changes he would make to the U.S. criminal code. When fellow Texan Beto O'Rourke declined to agree with Castro, sticking to the belief that illegally crossing the border should be, at least in some cases, a criminal offense, Castro was all over him. "I think that you should do your homework on this issue," Castro said to O'Rourke.

Earlier, Sen. Elizabeth Warren signed on to the decriminalization cause. That makes a majority of the Democratic field, and all of its front-runners, in favor of decriminalization.

Watching carefully Wednesday night was Brad Parscale, manager of President Trump's 2020 reelection campaign. "Now Democrats are for OPEN BORDERS!' Parscale tweeted. "These debates are great, the American people can now see how far left the candidates are. If these policies were implemented millions of foreigners would flood our system and overwhelm public services. They are disconnected from reality!" On Thursday, after the unanimous show of hands, Parscale returned to Twitter: "Democrats say: 'Open Borders!' Get here and we will let you in! So, let's just let all 7 billion people in. That will completely work. What???"

The Trump team was obviously delighted. But some Democrats were clearly concerned. On Thursday, former Obama strategist David Axelrod wondered, with a touch of dread, whether that night's debate would include a decriminalization discussion. "It will be interesting to see if @JulianCastro proposal to decriminalize border crossings returns as an issue in tonight's round, and whether any candidate demurs," Axelrod tweeted Wednesday. "It was a great moment that mortally wounded @BetoORourke. Long-term, however, it's a huge election target."

The topic did return, and no candidate demurred. And Parscale's reaction showed that it is indeed a huge election target.

And not just an election target. Castro's repeal proposal could turn U.S. border enforcement upside down. "If [the law] were repealed, it would be open borders," said Jessica Vaughan of the Center for Immigration Studies, which favors more restrictive policies. "There would be no basis for enforcing immigration law against those who come in illegally, not just for family and child illegal migrants, but also for criminals."

Democrats did not stop with opening the border. On Thursday night, they also unanimously supported a policy of offering healthcare to everyone in the country illegally — thought to be about 11 million people. "Raise your hand if your government plan would provide coverage for undocumented immigrants," said NBC's Savannah Guthrie. All hands went up.

The combination of an open border and increased benefits for those in the country illegally could greatly increase the already-high number of border crossers and the inducement for more to come. Trump, at the G-20 summit in Japan, took quick notice. "All Democrats just raised their hands for giving millions of illegal aliens unlimited healthcare," he tweeted. "How about taking care of American Citizens first? That's the end of that race!"

Beyond Miami, other prominent Democrats were also taking up the decriminalization cause Thursday. House Speaker Nancy Pelosi told reporters that an immigrant overstaying a visa or violating other immigration laws "shouldn't be a crime." "There's a disagreement that anybody coming across the border is breaking the law," Pelosi said. "Not until there's been a determination as to whether they can stay or not, but just because they are coming across the border, they don't."

All that happened in just a couple of days. There is no indication it will be the end of such proposals in the Democratic race; after all, it is just the first debate in a long race. Castro started something big, and after Wednesday's and Thursday's debates, it might be hard for Democrats to turn back.