Boston Bombings Pull D.C.'s Attention Back to Terrorism

What was supposed to be a jam-packed week of controversial legislation on Capitol Hill was punctuated by moments of silence for the victims of the Boston Marathon bombings and trepidation as security was tightened in the hours after the attack at key locales in Washington.

"Thoughts & prayers are with everyone in Boston," tweeted Sen. Chuck Schumer (D-N.Y.), a member of the Group of Eight. "Our bipartisan work on immigration will wait at least a day out of respect for the victims."

Whip counting continued at a quiet yet frenzied pace for the background check compromise of Sens. Pat Toomey (R-Pa.) and Joe Manchin (D-W.Va.), expected to come up for a vote this week as the first amendment of the gun control bill, but indications were that they lacked support and may have to go back to the drawing board.

Both chambers paused to remember the victims even as details remained hazy in the early evening hours. "I hesitate to call what the event was but clearly it was a terrible tragedy," Boston Rep. Mike Capuano (D-Mass.) said on the House floor, adding "whether official terrorism or unofficial" the attack was committed by "an evil person." House Speaker John Boehner (R-Ohio) ordered flags over the Capitol to be flown at half-staff.

The worst attack on U.S. soil since 9/11 was poised to dramatically shift the predefined agenda of the 113th Congress after a campaign season where the president said al-Qaeda was on the run and national security ranked low for voters concerned with economic recovery.

"I’ve updated leaders of Congress in both parties, and we reaffirmed that on days like this there are no Republicans or Democrats -- we are Americans, united in concern for our fellow citizens," President Obama said in an early evening statement in the briefing room.

"We still do not know who did this or why. And people shouldn’t jump to conclusions before we have all the facts. But make no mistake -- we will get to the bottom of this," he continued. "And we will find out who did this; we'll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice."

The White House released a photo of Obama on the phone in the Oval Office with FBI Director Robert Mueller. The FBI asserted federal jurisdiction to swiftly take over the investigation, with the bureau calling it a criminal investigation and "potential" terrorism investigation.

There was no alert issued from the National Terrorist Advisory System, which was the administration's replacement for the Bush-era color-coded terror alert system -- but there's never been an NTAS alert since the system began nearly two years ago.

“Our thoughts and prayers go out to everyone impacted by this incident in Boston, especially the families and loved ones of those injured," Homeland Security Secretary Janet Napolitano said in a statement. "Federal, state, and local law enforcement agencies continue to respond, and at the President’s direction, the Department of Homeland Security is providing any support necessary in this ongoing investigation. We encourage the public to be vigilant, and to listen to direction from state and local officials.”

As of Monday evening, three people were confirmed dead, including an 8-year-old boy, and more than 140 were injured, including 8 children, in a pair of sequential bombings at the finish line of the Boston Marathon. Reports indicated ball bearings were packed in the explosive devices.

The April 15 date of the attack touched off rampant speculation about motive and timing: It was Patriots' Day in Boston, as well as tax day nationwide. It was Israel's 65th Independence Day. It was Kim Il-Sung's 101st birthday. It was the day the U.S. bombed Libya in 1986.

But target-wise, it was an internationally recognized event with inherent controlled chaos where Bostonians off work and school for the civic holiday were gathered for an annual tradition.

"As this situation continues to develop and our first responders continue their effort to ensure the safety of our friends and family in Boston, there are still far more questions than answers," said Sen. Mo Cowan (D-Mass.), who was appointed to John Kerry's seat after the longtime senator became secretary of State.

Senate Homeland Security and Governmental Affairs Committee Chairman Tom Carper (D-Del.) said members were carefully monitoring the incident as it unfolded.

"In the end, we’ll get to the bottom of this incident and use any and all information from this horrible tragedy to bolster our security and response efforts and continue to do all that we can to keep events like this from happening again," he said.

And that turned to franker talk of terrorism among many lawmakers.

"Our first responsibility is to secure the support the victims and their families will need in the days and months ahead," said Sen. Jerry Moran (R-Kansas). "We must identify those who committed this cowardly act, as well as those who encourage them through actions or silence, and hold them fully accountable for their crimes.”

"Though it remains unclear who is responsible, this attack is yet another stark reminder that we must remain vigilant in the face of continuing terrorist threats," said House Foreign Affairs Committee Chairman Ed Royce (R-Calif.).

“While it's hard for us to imagine the kind of callousness necessary to so recklessly maim and kill innocents at such a wholesome event, we will not rest until the person or persons responsible for this tragedy are brought to justice," Sen. John Hoeven (R-N.D.) said.

Sen. Dianne Feinstein (D-Calif.), chairwoman of the Senate Intelligence Committee, told ABC News that the bombings had the "hallmarks" of terror attack. "It could be foreign, it could be homegrown," she added.

Senate Foreign Relations Committee Chairman Robert Menendez (D-N.J.) called on "my fellow members of Congress to use this attack on American soil to re-commit our commitment to protecting Americans at home and abroad.”

"I am disturbed and saddened that anyone would ruin this day of celebration by targeting innocent people and murdering them in cold blood," Sen. Marco Rubio (R-Fla.) said. "Once it is determined who is responsible, justice must be served to the fullest extent possible.”

Rep. Sheila Jackson Lee (D-Texas), a member of the House Homeland Security Committee, said she's "sure" congressional hearings will be called "when the investigations are complete."

"Within the next few months we must reevaluate the status of the safety and security of America’s large venues and large events that are coming up in the pending weeks and months," she said.

Homeland Security Chairman Mike McCaul (R-Texas) said he was in contact with Boston authorities and federal officials to try to get information about who's responsible as it becomes available.

"I would urge the American people to remain calm but vigilant," McCaul said. "Today's events are a stark reminder that our enemies continue to plot against us."