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KNOW IT ALL: Tuesday's Top 7 Stories at NBC News

From a shark attack to a website hack, see the stories we're following today.

Good morning. Here are some of the stories we’re following today:

1. U.S. Has Made 'Irreversible' Step with Cuba: Kerry

Secretary of State John Kerry told NBC News' Andrea Mitchell on Monday that GOP opposition to normalized relations with Cuba "just doesn't make sense." Republicans in Congress have vowed to cut off financing for the reopened U.S. embassy in Havana and block approval of a Cuban ambassador. Kerry, however, said the reconciliation between Washington and Havana is "irreversible." The same goes for the Iran nuclear deal, he said. Read more in NEWS.

2. FBI Searches Apartment of Chattanooga Shooter's Friends

FBI agents on Monday raided the apartment of two people who knew Mohammad Abdulazeez, the gunman who killed four Marines and a sailor at two military centers last week. The investigators are trying to determine whether the friends had any information on an attack plan. Read more in NEWS.

3. D.A.: It's 'Too Early' to Know How Sandra Bland Died in Cell

Jail authorities say civil rights activist Sandra Bland killed herself in a jail cell after she was arrested for allegedly assaulting an officer during a traffic stop. But the Waller County District Attorney said his office will investigate the case as thoroughly as it would a murder investigation. He said it was "too early to make any kind of determination that this is a suicide or a murder." Read more in NEWS.

4. Shark Attack Surfer Calls Quick-Responding Buddy a 'Warrior'

Professional surfer Mick Fanning said his friend who rushed to try to rescue him when two sharks attacked him during a competition Sunday is a "warrior." Fanning said he yelled to his fellow finalist, Julian Wilson, to "get in" to shore when the sharks attacked, but Wilson swam toward him in an effort to help instead. Both men were unharmed. Read more in NEWS.

5. Delta's Making a Big Change in Reward Miles Program

In less than a year, Delta will get rid of its fixed system of trading in miles for a free flight, and base the amount of miles needed on demand. "The number of miles needed (for a free flight) will change based on destination, demand and other considerations," beginning on June 1, 2016, Delta announced. Read more in BUSINESS.

6. Ashley Madison Users May Be at Risk of Blackmail After Hack

The hack of adultery website Ashley Madison could leave people at risk of blackmail, even if their information is only posted online for a short time. The damaging information "could easily be used as leverage not just for financial gain, but to influence decisions by any of those victims," said Chase Cunningham, a threat intelligence expert. Read more in TECH.

7. Where Was Trump When McCain Was a Prisoner of War?

Donald Trump's controversial claim that Sen. John McCain is not a war hero has sparked outrage. Critics have pointed out that while McCain was locked in a North Vietnamese prison cell, Trump was on his way to an Ivy League degree. Watch more in NEWS.

8. Nightly Spotlight: Lawyer Has Helped Hundreds of Foster Kids

Fostering 29 children is no simple feat, but for a lawyer in Kansas, providing a home for more than two dozen kids over the years was the relatively easy part. He's also helped more than 1,000 kids find permanent homes by using his legal knowledge to help foster parents adopt — for free.