Know It All: Monday evening's top stories from NBC News

President Barack Obama speaks with Savannah Guthrie on Monday. NBC News

Here's a snapshot of some of the top stories we're following Monday evening:

Obama isn't certain he'll order strike on Syria — or even win congressional authorization

In an interview with NBC News' Savannah Guthrie, President Obama said he hasn't decided whether he'll order military action against President Bashar Assad's regime in Syria — and he's not entirely certain he'll win a vote in Congress on a resolution to authorize a strike. "I wouldn't say I'm confident," he said. Read more on NBC News.

And he's skeptical about a Russian proposal for Syria to hand over its chemical weapons

Russia's foreign minister Monday suggested the turnover and destruction of Syria's chemical weapons arsenal as a means of averting U.S. strikes. And while Obama said that plan "represents a potentially positive development," he also appeared to downplay its importance, saying: "I think you have to take it with a grain of salt initially." Read more on NBC News.

Police respond to alleged dispute between George Zimmerman and his wife

Florida authorities are probing a confrontation between Zimmerman and his wife, Shellie, who called police Monday and said her husband threatened her with a handgun and attacked her father. "I'm really, really scared," she can be heard saying in a 911 call obtained by NBC News. But Zimmerman's wife and her father have decided not to press charges, according to officials. Read more on NBC News.

Bay Area wildfire chars more than 3,700 acres

Hundreds of responders battling the so-called Morgan Fire made some gains Monday — bringing containment of the blaze up to 20 containment — but the fire continues to expand. "The fire has grown significantly," an official said. It's just the latest front in California's summer-long fire fight. Read more on NBC News.

Tropical Storm Humberto could be the first Atlantic hurricane of the 2013 season

As it cuts a westward path across the Atlantic, Humberto is poised to become a hurricane within one day, according to the U.S. National Hurricane Center. Tropical Storm Humberto’s maximum sustained winds climbed to 50 mph on Monday afternoon, according to the Associated Press. Read more on NBC News.

Record-breaking swimmer Nyad ready to face skeptics

Long-distance swimmer Diana Nyad is slated to come face-to-face with a group of marathon swimmers who have raised doubts about whether the 64-year-old completed her crossing of the Florida Straits honestly. She'll hold a panel discussion via Skype on Tuesday evening. Read more on NBC News.

Bus plummets off cliff in Guatemala, killing dozens — including children

At least 41 people were killed, including children, after a bus plummeted off a cliff in rural Guatemala, Guatemala's General Department of Transportation said. The bus plunged some 650 feet into a river at the bottom of a ravine, according to officials. Read more on NBC News.