'Start Here': Mueller objects to Barr's summary of his findings, chaos in Venezuela, Facebook looks inward

It's Wednesday, May 1, 2019. Let's start here.

1. Mueller's letter about Barr's letter about Mueller's report

Attorney General William Barr is set to be grilled on Capitol Hill over his handling of Robert Mueller's report, including new reporting that Mueller raised objections to Barr's initial characterization of the special counsel's findings.

In a March 27 letter to Barr, Mueller wrote that the attorney general's four-page summary for Congress, which stated the special counsel reached no conclusion on any potential obstruction of justice by President Donald Trump, "did not fully capture the context, nature and substance of this office's work and conclusions," sources told ABC News, confirming an earlier report by The Washington Post.

"That is just a stunning rebuke from the special counsel to an attorney general tasked with overseeing him," ABC News' Alex Mallin says today on "Start Here." "It's worth reminding that Barr was appointed by Trump in the closing months of this investigation, which had already sparked concerns from Democrats that he was appointed just to protect this president."

The Department of Justice confirmed Barr received the letter and had a "cordial and professional" phone conversation with Mueller, noting in a statement: "The Special Counsel emphasized that nothing in the Attorney General's March 24 letter was inaccurate or misleading. But, he expressed frustration over the lack of context and the resulting media coverage."

Democratic lawmakers on Monday repeated calls for releasing Mueller's full, unredacted report and for the special counsel to testify. House Judiciary Committee Chairman Jerry Nadler also demanded the Department of Justice hand over Mueller's letter to Congress before 10 a.m. today.

2. 'A bloody day by all accounts'

Chaos unfolded in the streets of Venezuela on Monday as thousands of opposition protesters clashed with forces loyal to President Nicholas Maduro.

The protests on Monday lasted for hours as both sides battled with gunfire, tear gas and fire bombs. Interim leader Juan Guaido called on the armed forces to break ranks in a three-minute video, declaring it the "final phase" to oust the president.

Maduro demanded his forces stop any uprising, and by the end of the day, it appeared Guaido had not gained the military's loyalty, according to ABC News Chief National Correspondent Tom Llamas.

"It was a bloody day by all accounts," Llamas tells us. "The problem is, it looked like the military was still in power, and there were not the mass defections like Guaido had predicted and had called for."

Last night in a video address to his supporters, Guaido said it was a "historic" day for Venezuela and urged protesters to take to the streets a second day.

3. Private parts

"The future is private," Facebook CEO Mark Zuckerberg said at the company's F8 conference, announcing a major redesign for a "private social platform."

Facebook is "reprioritizing," according to Taylor Lorenz, a tech reporter for the Atlantic, by shifting away from a "News Feed" and toward "Groups" that focus more on connections with friends and family.

"The irony is that Facebook has always been a private place, and the move toward 'Groups' actually opens people up a lot more than you'd imagine," Lorenz says on the podcast. "It's really critical for the company's growth that people are on there making new connections, meeting new people."

"Start Here," ABC News' flagship podcast, offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, iHeartRadio, Spotify, Stitcher, TuneIn or the ABC News app. Follow @StartHereABC on Twitter, Facebook and Instagram for exclusive content and show updates.

Elsewhere:

'This is the worst day in the history of UNC Charlotte': At least two people die in a school shooting.

'No plans for the character': Jussie Smollett remains under contract, but don't expect to see him in the sixth season of "Empire."

'I believe that the position really shouldn't be a gendered position': The University of Southern California's marching band will have its first female drum major.

'Big and bold': Democrats and the president agree on a multi-trillion-dollar infrastructure plan that they describe using words typically reserved for new Taco Bell menu items or new flavors of Doritos or new Taco Bell menu items containing new flavors of Doritos.

From our friends at FiveThirtyEight:

Messi is more dominant than ever -- and Barcelona is more dependent: In some ways, Liverpool's task on Wednesday while facing Barcelona in the Champions League semifinal is simple. All the Reds likely have to do to reach a second consecutive European final is contain Lionel Messi, the greatest soccer player of all time.

Doff your cap:

To the colleagues of Alabama high school teacher David Green who donated 110 sick days so he and his wife could focus on caring for their cancer-stricken young daughter, we doff our caps.

Year-old Kinsley was diagnosed with leukemia in October. She's been undergoing chemotherapy, and even after enduring a few more rounds is expected to require outpatient chemo for two more years.

"Thank you for allowing us to be a family," Megan Green told "Good Morning America." "Thank you for the little bit of normalcy these days have provided."