How secure? White House considers increasing protection after an intruder reaches the mansion

President Barack Obama is "obviously concerned" about a weekend White House breach by an ex-soldier with a small knife who scaled a fence, sprinted across the lawn and entered the mansion before being arrested, a spokesman says.

The Secret Service increased its security on Monday around the perimeter of the White House, the presidential residence and one of the government's enduring symbols, while investigating how officers had allowed the incident to happen.

The breach led to a rare evacuation of much of the White House. Obama and his family were headed to Camp David when the breach occurred Friday evening.

White House spokesman Josh Earnest said the Secret Service investigation will include a review of protective efforts both inside the White House grounds and outside the fence line along Pennsylvania Avenue, including staffing and threat assessment policies and procedures.

Omar J. Gonzalez, a 42-year-old Army veteran from Copperas Cove, Texas, faces charges of entering a restricted building or grounds while carrying a deadly or dangerous weapon. The Army says Gonzalez served from 1997 until his discharge in 2003, and again from 2005 to December 2012, when he retired due to disability.

He was to appear in federal court later Monday.

Homeland Security Secretary Jeh Johnson said he would ultimately review the findings of the investigation ordered by Secret Service Director Julia Pierson. Johnson said the public should not rush to judgment about the security breach and urged against second-guessing security officers whom he said "had only seconds to act."

The Secret Service didn't open fire on Gonzalez or send attack dogs after him.

Officers who spotted Gonzalez scale the fence quickly assessed that he didn't have any weapons in his hands and wasn't wearing clothing that could conceal substantial quantities of explosives, a primary reason agents did not fire their weapons, according to a U.S. official briefed on the investigation.

Another consideration was whether bystanders behind the fence could have been injured by errant gunfire, said the official, who was not authorized to discuss the investigation by name and spoke only on condition of anonymity.

The Secret Service has long tried to balance public access to the "People's House" and security of the presidential residence.

The two-block stretch of Pennsylvania Avenue in front of the White House's north gates has been closed to vehicle traffic since May 1995, when President Bill Clinton ordered the immediate closure of the road in an effort to prevent a potential car- or truck-bomb attack.

On any given day, numerous uniformed officers can be seen patrolling parts of the sprawling lawns on either side of the White House, and others are stationed along the fence line on Pennsylvania Avenue. Monday morning, several officers patrolled the fence line, including one with a dog.

But the pedestrian-only zone hasn't entirely prevented security breaches along the fence or Pennsylvania Avenue.

Last September a man was arrested and accused of throwing firecrackers over the fence on the north lawn, near the area where Gonzalez is accused of climbing over the barrier. The Secret Service at the time said the man with firecrackers did not pose a threat.

A few weeks later a Connecticut woman set off a police chase through downtown Washington after ramming a security checkpoint near the White House. Miriam Carey, 34, was shot and killed by police near the Capitol.

In May, a man was arrested after he followed a motorcade carrying President Obama's daughters through the gates into the secure area near the White House. He had a pass for the Treasury Department, which is next door to the White House and also inside the pedestrian-only security zone. A charge of unlawful entry was later dismissed.

And in August a toddler managed to slip through the slats in the metal fence surrounding the White House. The Secret Service joked that they would wait until the boy learned to talk before questioning him.

Less than 24 hours after Gonzalez's arrest, a second man was taken into custody after he drove up to a White House gate and refused to leave, Secret Service spokesman Ed Donovan said. Bomb technicians in full gear searched the vehicle as agents briefly shut down nearby streets.

On Sunday, Secret Service spokesman Brian Leary identified the man as Kevin Carr, 19, of Shamong, New Jersey.

There was no indication the two incidents were connected. But they only intensified the scrutiny of the Secret Service, which is struggling to rehabilitate its image following a series of allegations of misconduct by agents in recent years, including agents on Obama's protective detail.

Sen. Tom Carper, D-Del., chairman of the Homeland Security and Government Affairs Committee, said he had spoken with Secret Service Director Pierson and was encouraged she would ensure the agency would use the incident as a "learning opportunity to reduce the likelihood that something of this nature will happen again."

House Homeland Security Chairman Michael McCaul, R-Texas, was to meet with Pierson later Monday.

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Associated Press writers Josh Lederman, Jessica Gresko and Julie Pace contributed to this report.