Trump announced the gunman's death and called Scalise, a 51-year-old Louisiana congressman, a good friend.
The shooter was identified as James T. Hodgkinson, a 66-year-old home inspector from IL who had several minor run-ins with the law in recent years and belonged to a Facebook group called "Terminate the Republican Party".
President Trump said on Wednesday morning that the shooter died of his injuries.
Until recently, he ran a home-inspection business out of his home in Belleville, in the southwestern corner of the state, across the Mississippi River from St. Louis, according to Hodgkinson's Facebook page.
Police in Alexandria, Va., said five people were provided medical transport and that a suspect was in custody. He was tended to by fellow lawmakers including Brad Wenstrup, a congressman who is a physician, before being transported to a hospital, where he was listed in critical condition.
"Everyone on that field is a public servant - our courageous police, our congressional aides who work so tirelessly behind the scenes with enormous devotion, and our dedicated members of Congress who represent our people", Trump said. "He was just walking and shooting", she said of the man, whom she described as white and wearing a T-shirt and shorts. A helicopter arrived to medevac at least one victim.
The shooting appeared to be a "deliberate attack", congressional and law enforcement sources said. "It would have been hard to miss me", he said.
Today, the Capitol Police force employs more than 1,700 officers who patrol the Capitol grounds and provide protective services to top lawmakers and their families.
And, under no circumstances, is it justifiable or acceptable - regardless of your current level of anger at Congress, President Donald Trump or any other government institution.
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I have obviously played him previous year semis here, played a really good match, played an incredible match against him in Rome. So is beating him this fortnight mission impossible? "I am not playing close to my best and everyone knows that".
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Among the announcements coming out of Apple's WWDC developer conference is news that Safari will prevent cross-site tracking. The Apple File System (APS) is not entirely new as it has appeared on macOS and other Apple devices since the WWDC 2016.
As of 9:45 a.m. ET, Scalise was in stable condition but undergoing surgery, according to a statement from his office.
The security service for the U.S. Capitol began with a single watchman when Congress first moved to Washington from Philadelphia in 1800. Gunshots hit the YMCA's windows, and the building was shut down and the block cordoned off, NPR's Tom Bowman reports from the scene.
"He was not injured", said Ashley Phelps, a spokeswoman for Rep.
"Our thoughts and prayers are with all affected", he said. After the man walked away, DeSantis said they alerted the police about him.
"We had three members of Congress take shelter in our apartment", he said on a live stream, as sounds of emergency vehicles could be heard. But I didn't take a picture of him and I heard somebody yell 'Get in the dugout!' And, the gunfire rang out.
We all - and no one is immune here - have to take a deep breath.
About 25 people had gathered for the Republican team's practice for an annual charity game, scheduled for Thursday night.
"I ask each of you to join me in resolving to come together, to lift each other up, and to show the country - to show the world - that we are one House".