Mueller testifies, Boris Johnson & a bison goes rogue in Yellowstone: The Morning Rundown

Good morning, NBC News readers.

Former special counsel Robert Mueller will take the hot seat this morning when he testifies before Congress.

Here's what we're watching today.

Four months after he sent his report on Russian interference in the 2016 election and the Trump campaign to Attorney General William Barr, Robert Mueller will testify publicly today about what his investigators did — and didn't — find.

• Here's a guide to everything you need to know about his testimony. When to watch, what to expect and who will be asking questions.
• What do the Democrats hope to get out of his testimony? They're hoping Mueller brings his dense 448-page report, that many Americans have not read, to life.
• If you'd like to read the full text yourself, here it is.
• Mueller won't be solo: He made a last-minute request for one of his longtime aides to sit alongside him as counsel.
• Analysis: Mueller has been a unique foil for President Donald Trump. If his congressional testimony is indeed damaging, the president will have to hope that his two-year delegitimization campaign of the decorated Vietnam veteran and former FBI director worked, writes NBC News' Jonathan Allen.
• The first hearing gets underway at 8:30 a.m. ET. Tune in for live coverage on NBC, MSNBC and NBCNews.com.

Immigration and Customs Enforcement arrested 35 people as part of an operation targeting families with deportation orders, officials said Tuesday, a number far lower than the 2,000 targeted in the highly publicized raids touted by Trump.

When asked about the low arrest rate, ICE Acting Director Matthew Albence said, "This is just the beginning of the operation."

ICE agents are under fire for smashing the driver's side window of a Missouri man, dragging him out and arresting him in a violent confrontation caught on tape Monday.

Today will mark the end of one era in British politics and the start of a new one.

Theresa May will face her final prime minister's questions in the House of Commons at 7 a.m. ET before she heads off to Buckingham Palace to tender her resignation to the queen.

Boris Johnson will then meet with the queen and she will invite him to form his government.

But the populist Conservative leader is not in for an easy ride. He faces perhaps the most daunting immediate challenge of any incoming British prime minister since Winston Churchill during World War II.

From Brexit to Iran, here's a look at the main challenges he'll face.

The Senate passed a bill Tuesday to ensure that a fund to compensate victims of the Sept. 11 terror attacks never runs out of money — and that first responders won't have to return to Congress to beg for more funding.

The vote came after intense lobbying from ailing 9/11 first responders — including one who died shortly after testifying before Congress last month.

"I'm hopeful that today begins the process of being able to heal without the burden of having to advocate," comedian Jon Stewart said.

A 9-year-old Florida girl was injured after a bull bison charged her and sent her flying into the air at Yellowstone National Park on Monday.

The unidentified girl was with a group of people in the Old Faithful Geyser area of the park in Wyoming.

The park service said the girl was "treated by a park emergency medical providers" and later released, but did not elaborate on the extent of the girl's injuries.

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• Neil Armstrong's family was paid $6 million by an Ohio hospital after the astronaut's death.
• Ivanka Trump misspelled United Kingdom in a congratulations tweet to Boris Johnson.
• Check out the battery behind the dangerous and deadly e-cigarette explosions.

"Once Upon a Time in Hollywood" is a three-hour reminder of Quentin Tarantino's blind spots, critic Noah Berlatsky writes in an opinion piece.

It's not just you thinking this summer is hotter than ever. An "unmistakable" climate trend is set to deliver Earth's hottest month on record, experts say.

Here's how to start a side hustle to make money without quitting your job. (Video)

"What I'm going to miss the most about D.C. is — nothing."

— Sept. 11th victims' advocate John Feal after the Senate passed the funding bill

One year from now, some 11,000 athletes will be in Tokyo for the start of the summer Olympics.

Here are some of the Team USA athletes to watch.

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Thanks, Petra