The assailant, prepared with "a lot of ammo," fought a gun battle with police before he was shot and later died. He has been identified as James T. Hodgkinson of Bellville, Illinois.
WATCH: Raw video of shooting on baseball field
Cell phone video captures dozens of shots being fired at Alexandria baseball field
RELATED: What we know about suspect in congressman shooting
Sen. Bernie Sanders said the gunman had been among the many volunteers on his presidential campaign.
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Rep. Jeff Duncan of South Carolina said he had just left the practice and encountered the apparent gunman in the parking lot before the shooting. The man calmly asked which party's lawmakers were practicing and Duncan told him they were the Republicans. The man thanked him.
Scalise dragged himself off the infield leaving a trail of blood as colleagues rushed to his assistance.
SEE FULL BASEBALL ROSTER BELOW
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 suspect, Alexandria police said. The shooter later died of his injuries, President Donald Trump told the nation from the White House.
"Everyone on that field is a public servant," Trump said. "Their sacrifice makes democracy possible."
Scalise, 51, the No. 3 House Republican leader first elected to the House in 2008, was in stable condition and undergoing surgery.
Who is Steve Scalise?
Who is Steve Scalise?
PHOTOS: Scene from shooting at Virginia park
Congressman Roger Williams'(R-Austin) office released a statement saying that one of his staff members, Zack Barth, was shot and is receiving medical attention. Williams was not shot. Barth is expected to make a full recovery.
Barth's father, Tim Barth, is on a flight to D.C. now, and told ABC13 reporter Tom Abrahams his son is "okay."
Paul Ryan called Tim to offer the family well wishes.
Who is Zack Barth: More on Houstonian shot in Virginia park attack
"Glad there were trained police staff on the premises to keep the situation from being much, much worse," Tim Barth said.
Rep. Mo Brooks (R-AL) described what he saw during the baseball game while he was at bat on the field:
"But I was on deck about to hit batting practice on the third base side and I hear, bam. And I look around and behind third base, in the third base dugout, which is a cinderblock, I see a rifle. And I see a little bit of a body," Brooks said. "At the same time I hear Steve Scalise over near second base scream. He was shot. Brooks took off his belt and myself and another congressman applied a tourniquet to try to slow down the bleeding."
Brooks said that the gun that he saw was a semi-automatic. He said a security detail shot back at the shooter and that there were at least 50 to 100 shots fired.
He said he heard people screaming from the dugout, "Shooter! Shooter! Active shooter!"
The shooting occurred at a popular park and baseball complex in Alexandria, where Republican lawmakers and others were gathered for a morning practice about 7 a.m. The annual face-off, which raises money for charity, was scheduled for Thursday evening at Nationals Park across the Potomac River in Washington.
Rep. Joe Barton is a representative from Texas. He talked about seeing the shooter and protecting his son who was there during the practice.
"I was getting down protecting, making sure my son was down," Barton said. "The heroes are the police officers who attacked the shooter and in doing so, quite probably, saved many, many lives," Barton said.
The Woodlands Congressman Kevin Brady was at the park Wednesday morning for practice and is okay, according to his public information officer. He left before the shooting.
Judge Ted Poe from Humble wrote on Twitter, "I'm horrified by the act of violence against Majority Whip Steve Scalise and several others this morning, Please..."
President Trump released a statement about the shooting this morning:
"The Vice President and I are aware of the shooting incident in Virginia and are monitoring developments closely. We are deeply saddened by this tragedy. Our thoughts and prayers are with the members of Congress, their staffs, Capitol Police, first responders, and all others affected."
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.
SOCIAL MEDIA REACTION:
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BASEBALL TEAM ROSTER OF DEMOCRATS AND REPUBLICANS
Democrats
Pete Aguilar (CA-31)
Nanette Diaz Barragan (CA-44)
Don Beyer (VA-08)
Brendan Boyle (PA-13)
Tony Cardenas (CA-29)
Joe Crowley (NY-07)
Joe Donnelly (IN - Sen.)
Mike Doyle (PA-14)
Ruben Gallego (AZ-07)
Jared Huffman (CA-02)
Hakeem Jeffries (NY-08)
Daniel Kildee (MI-05)
Ruben Kihuen (NV-04)
Chris Murphy (CT-Sen.)
Jimmy Panetta (CA-20)
Bill Pascrell (NJ-09)
Ed Perlmutter (CO-07)
Jared Polis (CO-02)
Cedric Richmond (LA-02)
Raul Ruiz (CA-36)
Tim Ryan (OH-17)
Linda Sanchez (CA-39)
Marc Veasey (TX-33)
Tom Suozzi (NY-03)
Eric Swalwell (CA-15)
Timothy Walz (MN-01)
Republicans
Joe Barton (TX-06)
Jack Bergman (MI-1)
Mike Bishop (MI-08)
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Kevin Brady (TX-08)
Mo Brooks (AL-05)
Mike Conaway (TX-11)
Ryan Costello (PA-07)
Rodney Davis (IL-13)
Ron Desantis (FL-6)
Jeff Duncan (SC-03)
Jeff Flake (AZ)
Chuck Fleischmann (TN-03)
Matt Gaetz (FL-01)
Bill Johnson (OH-06)
Trent Kelly (MS-01)
Darren LaHood (IL-18)
Doug LaMalfa (CA-01)
Barry Loudermilk (GA-11)
Roger Marshall (KS-1)
Pat Meehan (PA-07)
John Moolenaar (MI-04)
Steve Palazzo (MS-04)
Gary Palmer (AL-06)
Rand Paul (KY)
Erik Paulsen (MN-03)
Steve Pearce (NM-02)
Thomas Rooney (FL-17)
Dennis Ross (FL-15)
Steve Scalise (LA-01)
John Shimkus (IL-15)
Mark Walker (NC-06)
Brad Wenstrup (OH-02)
Roger Williams (TX-25)
Kevin Yoder (KS-03)
Stay with Eyewitness News as this story develops.
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