KNOW IT ALL: Friday’s Top 8 Stories at NBC News

Good morning. Here are some of the headlines we're following this morning:

1. More Than 1,000 U.S. Spies Protecting Rio Olympics

Hundreds of analysts, law enforcement and special operations personnel are already on the ground in Rio de Janeiro as part of a highly classified effort to protect the Rio 2016 Summer Games and American athletes and staff, NBC News has learned. Read more in INVESTIGATIONS.

Rio Olympics: Inside Brazil's Massive Security Operation 2:02

2. Sixteen Questions on Everyone's Lips as Olympics Begin

Even if you are not a diehard fan of gymnastics or track and field, there are plenty of intriguing storylines and inspirational stories worth following at this year's Olympics. And if you're still not convinced, at the very least the games should provide a small respite from the non-stop barrage of 2016 campaign headlines. Read more in SPORTS.

3. How to Watch the Olympics Without a TV

No TV? No problem! NBC is making 4,500 hours of Olympics coverage available at and the NBC Sports app. Read more in SPORTS.

4. More Prefer Democrats to Control Congress: Poll

Democrats hold a four-point lead in which party American voters want to control Congress, according to the latest national NBC News/Wall Street Journal poll. Forty-seven percent of registered voters prefer a Democratic-controlled Congress, while 43 percent prefer a GOP-controlled one. Read more in POLITICS.

5. How the GOP Would Fill A Vacancy on the Presidential Ticket

A flurry of controversies involving Donald Trump has led to questions about the immediate future of the party's ticket and what would happen if he were, for whatever reason, not on it. There is no indication that Trump is considering leaving the race or that there would be any attempt to remove him, but the party does have rules to deal with a vacancy on the ticket. Read more in POLITICS.

6. Zimmerman Claims Man Punched Him in Face at Restaurant

Sheriff's deputies are investigating an alleged assault on George Zimmerman, the Florida man acquitted of second-degree murder in the killing of Trayvon Martin, according to an investigative report obtained Thursday by NBC News. Read more in NEWS.

7. Husband Tries, Fails to Save Wife From Being Killed by Train

Police in Florida say a husband failed in his frantic attempt to pull his wife off railroad tracks after she tripped, and she was killed by an oncoming train. Read more in NEWS.

8. Strangled Runner Was Randomly Attacked, Sexually Assaulted

The NYPD says there is a "severe community threat" after the killing of Karina Vetrano, who left her Queens home to run in the park Tuesday afternoon and never came home. The department is offering a $10,000 reward for information leading to an arrest in the case. Read more at NBC NEW YORK.