5 Things to Know This Morning

— -- Your look at the five biggest and most buzz-worthy stories of the morning.

1. Law Enforcement Ramps Up Security for July 4th Weekend

Law enforcement agencies around the country say they are pulling out all the stops to make sure that this year’s Independence Day celebrations are not disrupted by a terror attack. The Department of Homeland Security and the FBI have issued a bulletin to authorities nationwide, warning that ISIS sympathizers may try to stage attacks and police are responding by beefing up security measures.

“Our nation is under threat, our law enforcement, our military are under threat, so we take the threat seriously,” U.S. Park Police Chief Robert MacLean said. However, no specific threats have been made.

An ABC News analysis shows that this year alone 40 people with suspected ties to ISIS have been arrested in the U.S. There have been seven arrests in just the last two weeks, including a group of ISIS believers who allegedly had plans to plant a bomb on the George Washington Bridge between New York and New Jersey.

2. Miss Universe Joins Chorus Slamming Donald Trump

The reigning Miss Universe joined a chorus of voices denouncing controversial remarks by the pageant’s owner, Donald Trump.

“I find Mr. Trump’s comments unjust and hurtful,” Paulina Vega wrote in an Instagram post. “As a Colombian and as Miss Universe, I want to show my support and validate the sentiments of the Latin community.”

However, despite outrage in Colombia over Trump’s views, Vega has said she won’t be giving up her crown, The Associated Press reported.

3. Woman With Amnesia and Battling Cancer Has Been Identified

A woman with amnesia and battling cancer who was found wandering in southern California has finally learned who she is after she and officials -- both at the local and international level -- spent months searching for her identity and family.

The woman, who called herself "Sam" since she was found by firefighters in Carlsbad, California, in February, has learned that she is Ashley Manetta, a 53-year-old woman who was born in Pennsylvania and later lived in Arizona and California, according to a Facebook page that has been leading efforts to reconnect her with her family.

4. Possible Explanation for Hillary Clinton Emails Secret 'Santa'

Was it really Christmas in July for former Secretary of State Hillary Clinton, or did it just seem that way because she happened to need a haircut?

Two emails released by the State Department earlier this week revealed that Clinton had meetings with an unidentified person referred to as “Santa,” raising published speculation about who that could be.

But the “Santa” in the emails may have nothing to do with the holiday. It actually may be Clinton’s hairdresser, who goes by that first name.

5. 'Back to the Future' Celebrates 30th Anniversary

Today marks the 30th anniversary of "Back to the Future" hitting theaters and launching Michael J. Fox into superstardom. In the film, Fox's character, Marty McFly, goes back in time to 1955 to change his father's past, while also saving his friend, time-travel inventor Doc Brown.

ABC News spoke to author, astrophysicist and cosmologist Neil deGrasse Tyson about the real-world possibilities of time travel, and got reflections on the movie from one of its stars, Lea Thompson.