A rifle-wielding attacker opened fire on Republican lawmakers at a congressional baseball practice Wednesday, wounding House GOP Whip Steve Scalise of Louisiana and several others as congressmen and aides dove for cover. The assailant, prepared with "a lot of ammo," fought a gun battle with police before he, too, was shot and later died.

"This is a stable situation," Michael Brown, chief of police for Alexandria, Virginia, told reporters. "At this point, there's no additional threat. We consider this incident to be a closed incident under investigation."

President Donald Trump made a surprise visit to MedStar Washington Hospital Center, where Rep. Scalise is being treated for his injuries following Wednesday's shooting at a Republican congressional baseball practice.

After undergoing surgery, Scalise remains in critical condition and will require additional operations to repair fractured bones, internal organ injury and severe loss of blood, MedStar Washington Hospital announced Wednesday night.

MedStar Washington said the congressman sustained a single shot to the left hip that traveled across his pelvis.

The president and first lady Melania Trump brought two bouquets of white flowers to the hospital, according to the Associated Press.

Authorities identified the gunman in Wednesday's shooting as James T. Hodgkinson, 66, of Belleville, Illinois.

Dramatic eyewitness video shows the incident unfold.

Gunfire erupts in the background of the video, which was obtained by the New York Post. A player is seen frantically running off of the field as two men ask aloud whether anyone has notified authorities of the shooting.

Sen. Bernie Sanders, I-Vermont, said on the Senate floor that the gunman apparently volunteered on his presidential campaign. Sanders said he was "sickened by this despicable act."

The gunman was believed to have driven to the baseball field in a large white van, Milton reports. The van with Illinois license plates was parked in a nearby parking lot.

Investigators are trying to determine if Hodgkinson was living out of the van. Witnesses have told investigators Hodgkinson was showering at a YMCA adjacent to the baseball field.

Rep. Jeff Duncan, R-South Carolina, told reporters that he had interacted with the gunman Wednesday morning right before the shooting happened.

"I did have an interaction with someone in the parking lot who asked me if the team practicing was a Democrat or Republican team," Duncan told reporters. "I told him they were Republicans. He said, 'K, thanks,' turned around. I got in the car and left, find out that my Republican colleagues were targeted by an active shooter today."

Duncan said that he believes the Republicans were targeted because of their political affiliation.

Related: Houston man among the wounded

Related: Politicians react to shooting in Alexandria, Va.

The gunman's weapon was similar to an M-4 assault rifle, CBS News has learned. The gunman had a rifle and "a lot of ammo," Flake said.

Scalise dragged himself off the infield leaving a trail of blood as colleagues rushed to his assistance.

Capitol Police officers who were in Scalise's security detail wounded the shooter, who was taken into custody. In all, five people were taken to area hospitals, including the gunman, Alexandria police said. The shooter later died of his injuries, Mr. Trump told the nation from the White House.

"Everyone on that field is a public servant," Mr. Trump said. "Their sacrifice makes democracy possible."

Texas Congressman Joe Barton recounted for reporters what he witnessed while with his son at the baseball field.

Photos: Shooting in Alexandria, Va.

Scalise, 51, the No. 3 House Republican leader first elected to the House in 2008, was shot in the hip, his office said in a statement. House Majority Leader Kevin McCarthy told reporters that Scalise was out of surgery.

MedStar Washington Hospital Center said on Twitter that Scalise was in critical condition. Scalise's office told CBS News that his family was coming from Louisiana to Washington. Before surgery, Scalise spoke to his wife on the phone and was in good spirits, his office said.

Mr. Trump said on Twitter that Scalise "was badly injured but will fully recover."

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The other people shot include the gunman, Capitol Police Special Agent Crystal Griner, lobbyist Matt Mika and Zack Barth, a staffer for Rep. Roger Williams, R-Texas.

George Washington University Hospital in Washington, D.C., said one patient it was treating from the shooting had died. The hospital didn't identify the patient, but the announcement came after Mr. Trump said the shooter had died.

The hospital said another patient it was treating was in critical condition. CBS News has identified that patient as Mika, who was out of surgery. A former congressional staffer who now lobbies for Tyson Foods, Mika was at the practice as a volunteer coach, CBS News correspondent Kris Van Cleave reports.

U.S. Capitol Police Chief Matthew Verderosa said in a statement that Griner was shot in the ankle and was in good condition. Special Agent David Bailey suffered a minor injury and was treated and released, Verderosa said.

Authorities said in a joint statement that a second congressman sustained minor injuries during the incident. The congressman wasn't identified.

Williams coaches the GOP team, his office said in a statement. He said that Barth "is doing well" and has since been released from the hospital.

In a Wednesday evening press briefing, Rep. Williams entered the room on crutches with ankle injury. He described the shooting as something he will never forget and "there were a lot of heroes out there today." He was on the ballfield when the incident unfolded Wednesday morning.

"I was on the third base side hitting ground balls ... little did I know that the perpetrator was about 20 yards from me," he said.

Williams dived into the first base dugout for cover when shots rang out and when Barth was struck in the leg.

The shocking event left the Capitol horrified and stunned. The House canceled proceedings for the day.

The shooting occurred at a popular park and baseball complex in Alexandria, Virginia, where Republican lawmakers and others were gathered for a morning practice about 7 a.m. They were in good spirits despite the heat and humidity as they prepared for the congressional baseball match that pits Republicans against Democrats. The popular annual face-off, which raises money for charity, was scheduled for Thursday evening at Nationals Park across the Potomac River in Washington.

The team was taking batting practice when gunshots rang out and chaos erupted.

Scalise was fielding balls on second base when he was shot, according to lawmakers present, then dragged himself into the outfield to get away from the gunman.

According to a source, when Democratic members of Congress practicing at a different ballfield miles away heard of the shooting, they immediately stopped and said a prayer together, Milton reports.

In a brief interview in a Senate hallway, Senate Majority Leader Mitch McConnell said, "I think everybody handled it well and things seem to be under control."

Other lawmakers were stunned in the aftermath of the event, which raised questions about the security of members of Congress. While the top lawmakers, including Scalise, have security details, others do not and regularly appear in public without protection. The last time a lawmaker was shot was when Democratic Rep. Gabby Giffords of Arizona was hit in the head and grievously injured while meeting with constituents at a supermarket parking lot in 2011.

Following the Giffords shooting, lawmakers have held fewer open town halls and have been advised to increase security at such events.