WASHINGTON -- In the hours after a gunman opened fire on a group of Republicans practicing for a charity baseball game, Republicans and Democrats were united on Capitol Hill.

House Majority Whip Steve Scalise was among those who were shot. Matt Mika -- a former congressional staffer who now works as a lobbyist for Tyson Foods -- as well as Zachary Barth, a staffer for Rep. Roger Williams and two Capitol Police officers were wounded.

There was a show of force at the Capitol on Wednesday, with long security lines and armed patrols guarding a shaken Congress, CBS News' Nancy Cordes reports.

"We can't let haters win. And we won't," said U.S. Rep. Pat Meehan, R-Pennsylvania.

The shooting prompted a pause in partisanship.

"An attack on one of us is an attack on all of us," said House Speaker Paul Ryan, to applause from Congress.

"An attack on one of us is an attack on all of us," said House Speaker Paul Ryan after Wednesday's shooting. CBS News

The attack wounded a very well-known member. As Majority Whip, Scalise is responsible for counting votes and changing minds -- a role reserved for those with the power of persuasion.

"He loves this place," said Sen. John Neely Kennedy, R-Louisiana. "I've never seen him in a bad mood -- I know he must be, he's human."

Unlike Scalise, most rank and file members do not have a security detail.

Rep. Claudia Tenney, R-New York, got this menacing email today: "One down, 216 to go..."

And a man who threatened Rep. Martha McSally, R-Arizona, will be arraigned this week.

"When you see some of the things that going on out there, it's like the frog in the water where you're turning the temperature up one degree at a time," McSally said. "And as I said when the man was arrested for making threats against me, threats of violence and active violence are not so far apart."

Some members asked today whether they could use campaign funds to pay for more protection.

Sen. Claire McCaskill, D-Missouri, said she's not sure that's the answer.

"At the end of the day, I like that I drive to the grocery store, and talk to women and men in the produce department about what's going on," McCaskill said.

Many lawmakers argued they need to turn the microscope on themselves and dial down political rhetoric that has divided the nation.

"I implore all of us to remember that we are first Americans," said Sen. Tim Scott, R-South Carolina.

After the shooting, an often polarizing president delivered a message of unity, CBS News' Margaret Brennan reports.

"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," Mr. Trump said.

The attack is the most high-profile act of domestic political violence on his watch. Mass shootings have become an unfortunate but repeated tragedy for recent American presidents.

Known for his often direct, off-the-cuff style, Mr. Trump chose his words carefully after speaking with Scalise's wife.

His speechwriter, Stephen Miller, was editing the remarks until moments before Mr. Trump delivered them, with his daughter Ivanka and son-in-law Jared Kushner standing nearby.

"We are strongest when we are unified and when we work together for the common good," Mr. Trump said.

A White House official said Mr. Trump is very aware of the delicate nature of what was unfolding Wednesday morning. Mr. Trump worked on his remarks with Vice President Mike Pence, someone who served in Congress himself, to craft a speech that showed reverence and respect for the victims.

It's still unclear if the gunman suffered from any mental health issues, but it appears his fury was fanned by what has become incendiary rhetoric of American politics.

In the wake of the shooting, Republicans and Democrats both called for civility, CBS News' Major Garrett reports.

"We do well at times like these to remember that everyone who serves in our nation's capitol is here because above all they love our country," Mr. Trump said.

"We respect you and your constituents who sent you here," said House Minority Leader Nancy Pelosi, D-California.

But partisan unity has been lacking for years.

During the campaign, Mr. Trump used incendiary language to describe his Democratic opponent, Hillary Clinton, calling her a "bigot."

"Such a nasty woman," he said in a debate.

She, in turn, called Mr. Trump's supporters deplorable.

"They're racist, sexist, homophobic, xenophobic," Clinton said.

The heated rhetoric has continued since Trump's inauguration. Comedian Kathy Griffin posted a photo of a decapitated Mr. Trump on social media. And a New York City production of Julius Caesar depicted the assassinated emperor as a Trump lookalike.

Shortly after the shooting, New York Republican Rep. Chris Collins pointed the finger at Democrats.

"I can only hope that the Democrats do tone down the rhetoric. The rhetoric has been outrageous in the anger directed at Donald Trump," Collins said.

But later, he said fault lies with both sides.

"And I think all of us can be a little introspective now. I will be, I promise you. To just say, let's just notch it down just a couple of decibels," Collins amended.

As law enforcement tried to learn if there was distinct political motive behind Wednesday' shooting, voices in Congress said no political grievance could justify violence. In the harrowing aftermath of all this, Republicans and Democrats appeared inclined to cool the rhetoric and ease the sense of division.