WASHINGTON (CBS NEWS) -- A top House Republican, Steve Scalise of Louisiana, was shot and critically wounded by a rifle-wielding gunman Wednesday at a congressional baseball practice just outside of Washington. At least four other people were also shot in addition to the gunman, CBS News has learned.

In a nationally broadcast address from the White House, President Trump said the gunman died from his injuries. CBS News has confirmed the gunman has been identified by law enforcement as James T. Hodgkinson, 66, of Belleville, Illinois.

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

The gunman's weapon was similar to an M-4 assault rifle, CBS News has learned. Sen. Jeff Flake, R-Arizona, described the gunman to reporters as a middle-aged white male wearing a blue shirt and possibly jeans.

"My view of him was just quick behind the dugout, and then when I realized he had a line of sight into the dugout with all the members there then we obviously went back down quickly," Flake said.

Capitol Police said officers who were part of Scalise's security detail returned fire and wounded the shooter, who was taken into custody.

"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."

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Related: Politicians react to shooting in Alexandria, Va.

Rep. Jeff Duncan, R-South Carolina, told reporters that he had interacted with the shooter 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.

Scalise was shot in the hip, his office said in a statement. House Majority Leader Kevin McCarthy told reporters that Scalise was out of surgery. According to the Associated Press, the hospital says that Scalise is in critical condition following surgery.

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

Photos: Shooting in Alexandria, Va.

The other people shot include the gunman, two Capitol Police officers, Matt Mika, a former congressional staffer who now works as a lobbyist for Tyson Foods, and Zachary Barth, a staffer for Rep. Roger Williams, R-Texas.

Williams was not injured in the incident, his office said in a statement. Mika was at the practice as a volunteer coach, CBS News correspondent Kris Van Cleave reports.

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Brown said five people were transported from the scene for medical reasons, but he wouldn't provide details on their conditions. George Washington University Hospital in Washington, D.C., said it was treating two patients in critical condition. U.S. Capitol Police Chief Matthew Verderosa told reporters that his injured officers were in good condition and had not suffered life-threatening injuries.

In a statement earlier, Mr. Trump said he and Vice President Mike Pence were monitoring developments closely.

"We are deeply saddened by this tragedy," Mr. Trump said. "Our thoughts and prayers are with the members of Congress, their staffs, Capitol Police, first responders, and all others affected."

The shooting occurred at a baseball field in Alexandria, Virginia, where lawmakers and others were gathered for a morning practice.

"We were doing batting practice," said Flake. "All of a sudden we heard a very loud shot. The gunman was over by the third base dugout with a clear view of the field." He said the gunman had "a rifle of some sort ... a lot of ammo."

Flake said the gunman was initially out in the open.

"Marty, our photographer, saw him raise the gun for the first time, the rifle, but he said he thought, 'Why in the world is somebody bird-hunting out here at this time,'" Flake said.

Rep. Mike Bishop, R-Mich., said Scalise was at second base when he was shot.

"I was looking right at him," Bishop told CBS Detroit radio station WWJ. "He was a sitting duck."

Rep. Mo Brooks, an Alabama Republican, said two law enforcement officers were believed to be among the others shot.

Brooks said that Scalise, 51, was down on the ground with what Brooks described as "a hip wound." The Alabama lawmaker said his colleague "crawled into the outfield, leaving a trail of blood."

"We started giving him the liquids, I put pressure on his wound in his hip," Brooks said.

The practice was for a bipartisan baseball game scheduled for Thursday. 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, CBS News senior investigative producer Pat Milton reports.

House Speaker Paul Ryan's office said Scalise's wounds were not believed to be life-threatening and that a member of the security detail was also shot.

Scalise is the No. 3 House Republican leader. He was first elected to the House in 2008 after serving in the state legislature.

Katie Filous was walking her two dogs near the field when she heard "a lot of shots, probably more than 20." She said the shooting "went on for quite a while."

Filous said she saw the shooter hit a uniformed law enforcement officer, who she said was later evacuated by helicopter. She said the officer had gotten out of a parked car, drawn a handgun and shouted something to the gunman, who then fired.

Rep. Jeff Duncan said in a statement that he was at the practice and "saw the shooter."

"Please pray for my colleagues," Duncan said.