Sen. Bernie Sanders (I-Vt.) won Saturday's Nevada caucuses decisively, after winning the New Hampshire primary and essentially tying former Mayor Pete Buttigieg for first in Iowa. So Sanders is the Democratic frontrunner, and he also leads nationally in a new CBS News/YouGov poll released Sunday, drawing the support of 28 percent of Democratic primary voters. But Sen. Elizabeth Warren (D-Mass.) jumped to second place in the poll, at 19 percent followed by former Vice President Joe Biden (17 percent), former Mayor Mike Bloomberg (13 percent), and Buttigieg (10 percent).

Warren came in fourth place in the Nevada caucuses, but a large majority of Nevada Democrats cast their early ballots before Wednesday night's Democratic presidential debate, and half the respondents in the CBS poll — taken Feb. 20-22, between the debate and the caucuses — were most impressed with Warren's performance. Warren's campaign also reported raising $14 million between the New Hampshire primary and Saturday.

CBS News has Biden leading in the next primary, South Carolina, but the big test will be Super Tuesday, March 3. And only 42 percent of Democratic primary voters have definitely made up their minds about who they will vote for, the poll found. At the same time, 69 percent of Warren's supporters are enthusiast about her candidacy followed by Sanders (65 percent), Biden (53 percent), and Buttigieg (52 percent). Democratic voters pick Sanders (57 percent) and Warren (53 percent) as the candidates who will fight the most for people like them.

A majority of all surveyed voters told CBS News/YouGov that President Trump will definitely (31 percent) or probably (34 percent) win re-election, even though in hypothetical head-to-head matchups, Sanders, Biden, and Warren all narrowly beat Trump.

YouGov conducted the poll Feb. 20-22 among 10,000 registered voters, including 6,598 Democrats and Democratic-leaning independents likely to vote in the primary. The margin of error for the entire poll is ±1.2 percentage points and for the Democrats, ±1.7 points. Peter Weber

With their lights flashing and sirens blaring, fire trucks, ambulances, and police cars made their way through the streets of Osseo, Wisconsin, on Saturday, putting on a parade for kids celebrating their birthdays inside while in quarantine.

First responders with the Osseo Rural Fire Department, Trempealeau County Sheriff's Department, Osseo Police Department, and Mayo Clinic all participated.

Firefighter Chris Cuddy told WQOW that being in quarantine is "very hard on the children. They can't go to school to see their friends. They're having these birthday parties with just what they have at home and their friends aren't able to come. Maybe what we're doing today will bring some joy to them, make them a little bit happy on their birthday."

This wasn't a one-time only event — parents can request birthday parades for their children through the Osseo Rural Fire Department. Catherine Garcia

Irish Prime Minister Leo Varadkar is going back to his roots, with his office announcing on Sunday that once a week, he will work as a doctor in order to help patients during the coronavirus pandemic.

Varadkar spent seven years as a doctor, leaving the profession in 2013 when he became a politician. His office said he re-registered as a physician in March, and The Irish Times reports he will be assessing people over the phone, talking to them about their symptoms before they go to the hospital.

"Many of his family and friends are working in the health service," Varadkar's spokesman said. "He wanted to help out even in a small way." His father was a general practitioner, his mother was a nurse, and his partner is a cardiologist.

Ireland's health minister has asked former health care professionals to re-register and help staff up Ireland's Health Service Executive, and 70,000 people have responded, Reuters reports. Catherine Garcia

They've made full recoveries, and now it's time for koalas rescued during last year's devastating Australian bushfires to go back into the wild.

Science for Wildlife, a conservation organization in Sydney, released the first 12 koalas back into the Blue Mountains on March 25 and 27. Those koalas were saved in December and spent the last few months recovering at Sydney's Taronga Zoo. Dr. Kellie Leigh, Science for Wildlife's executive director, said in a statement that her team made sure conditions had improved enough to sustain the koalas.

"The recent rains have helped and there is now plenty of new growth for them to eat, so the time is right," Leigh said. "We will be radio-tracking them and keeping a close eye on them to make sure that they settle in okay."

On April 2, Port Macquarie Koala Hospital released a koala it rescued in October, and has plans to set 25 more koalas free in the next few days, The Independent reports. Sue Ashton, the hospital's president, said not only will the koalas go back to their home habitats, but in some cases, they will be returned "to their original tree." Catherine Garcia

U.S. officials and intelligence agencies started warning the White House in mid-January that the coronavirus outbreak in China could spread through the U.S. and around the world, but "the Trump administration squandered nearly two months that could have been used to bolster the federal stockpile of critically needed medical supplies and equipment," The Associated Press reported Sunday night. "A review of federal purchasing contracts by The Associated Press shows federal agencies largely waited until mid-March to begin placing bulk orders of N95 respirator masks, mechanical ventilators, and other equipment needed by front-line health care workers."

By mid-March, U.S. hospitals in hard-hit areas were treating a rising number of COVID-19 patients without adequate equipment, states were bidding against each other for masks and ventilators on the open market, and Trump was telling states the role of the U.S. stockpile was supplier of last resort. "The notion of the federal stockpile was it's supposed to be our stockpile," Jared Kushner, Trump's son-in-law and senior adviser in charge of coronavirus supply chains, said Thursday. "It's not supposed to be state stockpiles that they then use."

An AP reporter asked Trump about the federal supply shortfall at Sunday night's briefing, Trump dismissed the question and ended the briefing.

The federal emergency stockpile was created in 1999 to prepare for the Y2K issue, then was expanded after the Sept. 11, 2001, attacks and stocked up with pandemic response supplies in 2006. Greg Burel, director of the federal stockpile from 2007 until his retirement in January, told AP that based on budget allocations, it was intended only as a "bridge stock."

"States do not have the purchasing power of the federal government," said former Health and Human Services Secretary Kathleen Sebelius, who also served as governor of Kansas. "They do not have the ability to run a deficit like the federal government. They do not have the logistical power of the federal government." Now, she added, "we basically wasted two months." Read more at The Associated Press. Peter Weber

Public health experts and government officials agree that the U.S. government's coronavirus death toll almost certainly understates how many Americans have actually died from the virus.

The Centers for Disease Control and Prevention only counts deaths where the presence of the coronavirus is confirmed in a lab test, The Washington Post reports, and "we know that it is an underestimation," CDC spokeswoman Kristen Nordlund said.

There are many reasons why the numbers are underreported. Strict criteria in the beginning of the outbreak kept many people from getting tested for coronavirus, and it's still difficult to get tested in some areas, for example. There's also the matter of false positives, and not all medical examiners have tests or believe they should conduct postmortem testing, even on people who died at home or in nursing homes where there were outbreaks. Experts also believe some February and early March deaths that were attributed to influenza or pneumonia were likely due to coronavirus.

The official death count is based on reports sent by states, and as of Sunday night, the CDC reports 304,826 confirmed U.S. cases and 7,616 deaths. The Post, other media outlets, and university researchers update their numbers more frequently, with the Post reporting on Sunday night that 9,633 people have died from coronavirus in the U.S., and at least 337,000 cases have been confirmed. Catherine Garcia

A fight broke out in the White House Situation Room on Saturday, after President Trump's economic adviser Peter Navarro clashed with Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, over an unproven COVID-19 coronavirus treatment, Axios reports.

Four people with knowledge of the matter told Axios' Jonathan Swan the argument took place near the end of a White House coronavirus task force meeting, after Food and Drug Administration Commissioner Stephen Hahn brought up hydroxychloroquine, an antimalarial drug Trump has touted as a possible "game-changer" in the fight against coronavirus. When Hahn was finished giving updates on drug trials, Navarro put folders down on the table where Hahn, Fauci, Vice President Mike Pence, and others were sitting.

One person familiar with the conversation told Swan the "first words out of his mouth are that the studies that he's seen, I believe they're mostly overseas, show 'clear therapeutic efficacy.' Those are the exact words out of his mouth." Fauci responded that this was anecdotal evidence, and this "just set Peter off," Swan reports. Navarro pointed to the folders and said, "That's science, not anecdote," a source said, and as his voice continued to get louder, Pence tried to intervene. "It was pretty clear that everyone was just trying to get Peter to sit down and stop being so confrontational," another person told Swan.

Fauci and other public health officials have said more data is needed before anyone can say the drug is effective against COVID-19, but based on things he's read, Navarro is convinced it works, Swan reports. The task force ultimately decided that publicly, the White House needs to say that use of hydroxychloroquine is between doctors and patients. Read more at Axios. Catherine Garcia