As Hillary Clinton and Bernie Sanders' fight for the Democratic nomination winds toward a close, the pair of candidates leaves behind them a surprisingly friendly primary — perhaps the most gracious ever, at least in terms advertisements. According to Kantar Media, of the 206,528 ad spots Clinton and Sanders aired between them this year, not a single one was determined by analysts to be "negative."

"In an open presidential primary, this is probably unprecedented," Kantar's senior vice president for political advertising Elizabeth Wilner told Bloomberg.

Donald Trump, by comparison, faced $62 million in attack ads during the primary season. Obama and Clinton both aired negative ads against each other back in 2008, too. However, Sanders doesn't believe in attack ads — and Clinton both didn't see Sanders as a big enough threat and risked alienating his supporters in a general election by airing her own ads against him.

The goodwill might not last much longer, however. Clinton has no such qualms holding back against Trump — her campaign has already produced an ad slamming her likely general election opponent for attacking Judge Gonzalo Curiel in a racist manner. And, of course, Trump has never exactly been one to hold back on how he really feels. Jeva Lange

After the coronavirus pandemic slowed the momentum of anti-government, pro-democracy demonstrations in Hong Kong, the protest movement picked up steam again Sunday after Beijing signaled it would directly impose national security laws on the city. Now, many of the young protesters believe the only two outcomes are either independence or the loss of autonomy promised in China's 1997 territorial exchange with the United Kingdom.

If the latter takes place, U.S. National Security Adviser Robert O'Brien expects an economic fallout. Hong Kong, he said, has emerged as Asia's financial center because financial service firms and other businesses flocked to the city thanks to its democracy, free enterprise, and rule of law. If Hong Kong loses those defining characteristics, in O'Brien's view, because of a Beijing takeover, he can't envision how those companies can remain.

He also predicts that many Hong Kong citizens would seek a way out. "I think you're also going to have a terrible brain drain," he said. "I think Hong Kong citizens, many of whom can travel under certain circumstances to the United Kingdom or seek refuge in other places, they're not going to stay in Hong Kong to be dominated by the People's Republic of China and the Communist Party." Tim O'Donnell

Former Food and Drug Administration Commissioner Scott Gottlieb said Sunday that the coronavirus outbreak hasn't been "contained yet," but he did tell CBS's Margaret Brennan that he believes there will be a "seasonal effect" that may allow Americans to "enjoy some semblance of the lives they want to enjoy" particularly in the summer months of July and August as cases go down. Of course, people will need to continue practicing good hygiene and modified social distancing.

That said, he also anticipates that the virus will continue to circulate and eventually present a risk of causing epidemics in certain places in the U.S. during the fall and winter, so whatever reprieve comes in the summer may be short-lived.

As for what happens during that potential resurgence in the fall? Dr. Deborah Birx, one of the prominent members of the White House coronavirus task force, said it's "difficult to tell" if the U.S. economy will have to shut down again, but she said the government is trying to learn how to keeping things open safely. She said that "proactive" testing, including testing asymptomatic people, will prove key in developing a coherent strategy. Tim O'Donnell

President Trump and former Attorney General Jeff Sessions are back at it.

The pair went after each other over Twitter on Saturday, with Trump — who is backing Sessions' Alabama GOP Senate opponent Tommy Tuberville — saying Sessions showed "no courage" when he recused himself from investigations into 2016 Russian election interference.

Sessions fired back by refusing to apologize for "following the law and serving faithfully and with honor," though he also reiterated that he, not Tuberville, is the one actually fighting for Trump's agenda. So, despite his apparent dissatisfaction with Trump's words, he hasn't backed away from the president politically.

Before the Twitter sparring, Trump recorded an interview Friday with Sharyl Attkisson airing Sunday. During the interview, Trump similarly blasted Sessions, arguing that he was not "mentally qualified" to serve as attorney general and never should have gotten the job. Tim O'Donnell

Wang Yanyi, the director of the Wuhan Institute of Virology, told Chinese state media Sunday the lab was working on three live strains of bat coronavirus, but the closest genetic match to the virus that causes COVID-19 and sparked a global health crisis was only 79.8 percent. Therefore, Wang said, claims by the likes of President Trump and Secretary of State Mike Pompeo that the virus may have escaped from the facility are "pure fabrication."

As tensions between the U.S. and China have heightened since the outbreak, Trump and Pompeo have leaned into the lab-origin theory. But the scientific consensus remains that the pathogen was passed from bats to humans through an intermediary species at a wet market in Wuhan last year, although it's becoming more challenging to pinpoint the animal.

China's Foreign Minister Wang Yi said Sunday that some political forces in the U.S. are trying to push the two global powers "to the brink" of "a new Cold War" and endangering global peace. Wang's concerns were broader than just the back and the forth over pandemic blame, however; he also criticized the U.S. for slowing nuclear negotiations with North Korea and warned Washington not to cross Beijing's "red line" on Taiwan. Wang did say foreign interference concerning Hong Kong's renewed anti-government protests was unwelcome, but he didn't single the U.S. out in that regard. Read more at The Guardian and Bloomberg. Tim O'Donnell

Just days ago, scientists leading the University of Oxford's coronavirus vaccine development expressed optimism about their progress — more than 1,000 people in the United Kingdom have been inoculated already, and 10,000 more will be given the vaccine in May and June. But there's some cause for concern, The Telegraph reports.

Professor Adrian Hill, director of the University's Jenner Institute, said what was formerly an 80 percent chance of developing an effective vaccine by September — possibly in time for a potential second wave of infections — has dwindled to 50 percent. That's not because the team no longer believes in its work, which is reportedly still going well. Instead, the U.K.'s infection rate decline may make it tough to gauge the vaccine's efficacy. "It's a race against the virus disappearing, and against time," Hill said.

Hill only expects fewer than 50 of the 10,000 trial volunteers to catch the virus, which has faded since the U.K. and other countries implemented strict lockdowns, and if it turns out that fewer than 20 test positive, the study's results may be useless.

The vaccine showed promise when it was tested in six rhesus macaque monkeys earlier this year, but it will obviously need to show that it provides the same protection in humans before it can be distributed. Tim O'Donnell

Hong Kong's pro-democracy, anti-government protests were back in full force Sunday for the first time since COVID-19 lockdowns began, while riot police fired tear gas on the crowds for the first time in weeks.

Thousands of mostly young people took to the streets just days after China signaled it planned to directly impose national security laws against subversion, sedition and terrorism, and collusion with foreign forces on the city. The demonstrators believe Beijing's plan to bypass Hong Kong's local government and legislature violated the "one country, two systems" agreement it signed with the United Kingdom during a territorial exchange in 1997. The plan is backed by Hong Kong Chief Executive Carrie Lam but faced international condemnation.

China has denied the move will affect Hong Kong's autonomy, but many of the protesters now think independence — considered a red line by Beijing — is the only way forward. "I think this is the termination of one country, two systems," one protester told The Wall Street Journal. "Hong Kong is lost. The most important thing is to fight back against the Communist Party." Read more at The Wall Street Journal and Reuters. Tim O'Donnell