Treasury Secretary Steven Mnuchin notified House Democrats on Monday that he will not turn over President Trump's tax returns, claiming that the request from the Ways and Means Committee "lacks a legitimate legislative purpose."

Under a 1924 law, Ways and Means Chair Richard Neal (D-Mass.) is one of just a few lawmakers with the authority to request the president's tax returns, and he asked the IRS for six years of Trump's business and personal returns. In his letter to Neal, Mnuchin said he spoke with officials in the Justice Department and concluded the IRS is "not authorized to disclose the requested returns and return information." He did not explain their reasoning. The law in question does not require Neal to have a legislative purpose.

Democrats argue that to perform their oversight duties, they need to see Trump's tax returns, but Mnuchin says providing them could potentially violate Trump's right to privacy. This move will almost certainly trigger a legal battle, with Democrats expected to file a lawsuit in order to have a federal judge rule on the issue. Catherine Garcia

Rep. Alexandria Ocasio-Cortez (D-N.Y.) watched Tuesday night's Democratic debate, and one thing stood out to her.

"Not a single climate change question," she tweeted. "Horrifying." One of the participants, Sen. Bernie Sanders (I-Vt.), agreed, responding, "A disgrace." The Democratic candidates don't shy away from talking about climate change on the campaign trail; billionaire investor and environmentalist Tom Steyer told voters in South Carolina on Tuesday that climate change is his "No. 1 priority," and if elected, he will declare a climate emergency on his first day in office.

Poll after poll has shown that climate change is a key issue for voters; last week, the Pew Research Center released a survey showing that for the first time in two decades, a majority of Americans believe that tackling climate change should be a main priority for the president and Congress.

Another poll released last week by the nonpartisan nonprofit Climate Nexus found that for Democrats, climate change is one of the two most important issues facing the country right now. "This is the first time in American political history where climate change is not just a top-tier issue, it is the top-tier issue," Anthony Leiserowitz, a senior research scientist at Yale who helped conduct the poll, told The Atlantic. Catherine Garcia

In her response to why she would make a better president than Democratic frontrunner Sen. Bernie Sanders (I-Vt.) during Tuesday night's debate in South Carolina, Sen. Elizabeth Warren (D-Mass.) compared their plans to expand Medicare-style health care to all Americans. Sanders let his body do the disagreeing, and if this whole president thing doesn't work out, his face has enough expressiveness to anchor, say, an HBO show about a curmudgeonly old man who frequently throws up his hands at the world.

Here's Warren's full answer on why plans and legislative strategy matter, with her face included. Peter Weber

A 23-year-old American soldier based in South Korea has tested positive for the new coronavirus COVID-19, the U.S. military announced Tuesday.

The soldier is stationed at Camp Carroll in Waegwan, and is the first U.S. service member to come down with the virus. He is under quarantine at his home, which is off base.

There are 1,146 confirmed cases of COVID-19 in South Korea, with more than half of the patients living in the city of Daegu. The soldier visited a military base in Daegu on Friday, and then returned to Camp Carroll. There are 28,500 U.S. soldiers stationed in South Korea, and the military said health professionals are "actively conducting contact tracing to determine whether any others may have been exposed." Troops have been told to avoid nonessential meetings and stay on base, The New York Times reports. Catherine Garcia

Sen. Bernie Sanders (I-Vt.) defended himself against accusations that he is not "pro-Israel" enough, saying he is "very proud of being Jewish" but fully aware of the "suffering of the Palestinian people."

If elected, Sanders would be the first Jewish president. During Tuesday night's debate in South Carolina, he said he once briefly lived in Israel, and "what I happen to believe is that right now, sadly, tragically, in Israel, through [Prime Minister] Bibi Netanyahu, you have a reactionary racist who is now running that country. And I happen to believe that what our foreign policy in the Mideast should be about is absolutely protecting the independence and security of Israel. But you cannot ignore the suffering of the Palestinian people. We have got to have a policy that reaches out to the Palestinians."

Former New York Mayor Mike Bloomberg, who is also Jewish, said "the only solution here is a two-state solution. The Palestinians have to be accommodated. The real problem here is you have two groups of people, both of whom think God gave them the same piece of land. And the answer is to obviously split it up." Sen. Elizabeth Warren (D-Mass.) agreed that there has to be a two-state solution, and said President Trump favors Israel by "putting a thumb on the scale on just one side." Israelis "have a right to security," she said, just like Palestinians "have a right to be treated with dignity and have self-determination. ... But it's not up to us to determine what the terms of a two-state solution are. We want to be a good ally to everyone in the region." Catherine Garcia

Media insiders are labeling the South Carolina Democratic debate a "disaster" following a messy and often out-of-control evening that frequently devolved into shouting matches between the candidates. The event marked CBS News' first foray into hosting a debate this election cycle, and the moderators — CBS Evening News anchor Norah O'Donnell and CBS This Morning co-host Gayle King — often appeared to be overpowered by the seven candidates they were supposed to be keeping in line.

TV regulars at rival networks, including former DNC head and Fox News contributor Donna Brazile, Morning Joe's Mika Brzezinski, and The View's Meghan McCain, expressed horror over how the night unfolded:

Brian Stelter, the chief media corespondent for CNN, confirmed the industry's general reception of the debate:

Sean Illing of Vox was even blunter: "These are the worst moderators in the history of moderation," he tweeted. Jeva Lange

The recent comments made by Sen. Bernie Sanders (I-Vt.) about Cuba and its former leader Fidel Castro were bound to come up during Tuesday's Democratic primary debate in Charleston, South Carolina.

When the topic eventually made its way into the chaos, Sanders' fellow candidates zeroed in on his past praise for certain aspects of the Cuban government, such as its literary program and health care system. Sanders once again clarified he was merely pointing a few good things about the Castro regime, which he describes as otherwise authoritarian. But that wasn't good enough for his competitors.

Former South Bend, Indiana, Mayor Pete Buttigieg, for example, said such comments could have consequences for Democrats down the line, suggesting the party could lose House and Senate races because of them. "We're not going to win these critical, critical House and Senate races if people in those races have to explain why the nominee of the Democratic Party is telling people to look at the bright side of the Castro regime," Buttigieg said.

Sanders once again argued he has routinely condemned authoritarianism before pointing out that the U.S. government supports Saudi Arabia despite its human rights violations. Tim O'Donnell