House GOP Whip Steve Scalise is expected to have more operations after he was shot in the hip when a gunman opened fire on a baseball practice of Republican leaders at a Virginia park Wednesday morning.

As bullets rang out, Scalise was hit in the hip and three others were wounded by gunfire: a congressional aide, a lobbyist for Tyson Foods, and a capitol police officer, who was part of a detail protecting Scalise.

Colleagues said Scalise, who had been fielding balls at second base, dragged himself away from the infield, leaving a trail of blood before they rushed to his assistance.

"A lot of us ran into dugout for cover. And there was just pandemonium," described Arizona U.S. Sen. Jeff Flake.

Scalise was listed in critical condition Wednesday night at a Washington hospital, which stated he would require several more operations.

Others who were there expressed gratitude towards the two Capitol Police officers who were wounded.

"There could have easily been 25 deaths or more today. But officers (Crystal) Griner and (David) Bailey prevented that and my family and I will be forever grateful. The thin blue line held today ...," said Texas U.S. Congressman Roger Williams.

Bailey was treated for a minor injury and Griner was shot in the ankle.

The shootout ended when police took down the gunman, identified by law enforcement as 66-year-old James Hodgkinson of Belleville, Ill.

A former volunteer for U.S. Sen. Bernie Sanders's presidential campaign, Hodgkinson's social media is littered with anti-President Donald Trump sentiment, raising the possibility of a politically-motivated attack. He belonged to the Facebook group called "Terminate the Republican Party."

The Facebook group posted this message following news of the shooting.

"We do not condone violence in this group," posted Howard Scott Pearlman, an administrator of Terminate the Republican Party. "We support the Termination of The Republican Party by voting all Republicans out of office."

The FBI is not stating a motive yet, but is asking the public for help in the investigation. Sanders said he was "sickened by this despicable act."

"A gentleman walked up to us and wanted to know whether there were Republicans or Democrats practicing out there. Congressman (Jeff) Duncan said that it was Republicans," said Florida Republican U.S. Congressman Ron DeSantis.

Texas Rep. Mike Conaway described what sounded like an explosion, then lawmakers scattering off the field as police roamed in search of the gunman and engaged him.

“The guy’s down to a handgun, he dropped his rifle, they shoot him, I go over there, they put him in handcuffs,” Conaway said, adding that if the shooter had “gotten inside the fence, where a bunch of guys were holed up in the dugout, it would have been like shooting fish in a barrel.”

As Trump made a surprise visit to the MedStar Washington Hospital Center Wednesday evening to see Scalise, lawmakers prepare to take the field at National's Park on Thursday in a bipartisan show of force.

"If we don't play the ball game, they will think we lost our will. We will play the ball game, it's for charity and I hope that that stadium is filled to capacity," Williams said.

The Associated Press contributed to this story.