Obama will speak at a rally at USC, which will begin at 2 p.m. Both Boxer and Brown will be at the rally.
Obama arrived at LAX at about 11:30 a.m. The Secret Service and the LAPD wanted to minimize the traffic impact, so Obama flew to USC aboard Marine One instead of driving.
The last time Obama was in L.A. in August, he traveled from Hancock Park to LAX by car, turning a lot of streets on the Westside into parking lots.
Barricades were already in place on Figueroa Street for crowd control because officials are expected a crowd of about 30,000 people at the rally.
Thousands of people descended on USC's campus for a chance to see Obama, some lining up as early as 3 a.m.
"I've met him here in Los Angeles, and I'm here to continue my support for our president because I'm really impressed with the job that he's doing," said Melvin Orphey of Los Angeles.
Many USC students said they are pumped up for the rally even though there will be traffic tie-ups.
"I'm a freshman here at USC, so to find out that he's going to come here in my first few months just makes it so worth it," said student Dylan Purdy.
USC student Rayna Strasser-King said her mom left Palmdale at 2 a.m. to meet her on campus early.
"We're trying to get in line early because we hear it's going to be a big turnout," she said.
The rally starts at 2 p.m. at Alumni Park. The main streets will be shut down around campus for several hours.
"These are busy streets, so when you close them off or shut them down the problem gets displaced to streets in the surrounding areas. It radiates outward," said LAPD Lt. John Romero.
Drivers are advised to avoid Figueroa Street, Martin Luther King Jr. Blvd., Vermont Avenue and Exposition Boulevard. These streets will have soft closures starting at 9:30 a.m., which means they won't be open to through traffic. Only vehicles that absolutely have to get in will be allowed in.
Then from 11:25 a.m. to 2:50 p.m., there are hard closures, which mean no pedestrian or vehicular traffic on those streets until the president leaves campus for Glendale.
Obama's motorcade is likely to snarl traffic in the afternoon when the president heads to Glendale for a radio interview.