None of Tuesday’s climactic events in Congress will be happening as scheduled. Instead, the pace of Capitol Hill has been slowed considerably by enhanced security, and lawmakers are spending some of their extra time speculating — without many facts to go on — whether the Boston Marathon bombing was an act of domestic or international terror.

The central provisions of the bipartisan Senate immigration package were released overnight. But a triumphant news conference with 16 business and labor leaders was put on hold in deference to the bombings, and the first hearing on the bill was put off until Friday. The Senate vote on expanding background checks for gun purchasers has also been postponed, in part because sponsors concluded it would be unseemly to have that roll call a day after the bombings, but mainly because they have not found the 60 votes they need to win.

The casualty count now stands at three dead and 176 injured by the two bombs that detonated near the finish line, a dozen seconds apart, the first multi-victim bombing on American soil since 9/11. Massachusetts Gov. Deval Patrick said Tuedsay morning that no unexploded bombs were found in a search of downtown, much of which remains cordoned off.

President Barack Obama ordered flags on federal buildings lowered to half-staff and was briefed by his counterterrorism adviser Lisa Monaco, FBI Director Robert Mueller, Attorney General Eric H. Holder Jr. and Homeland Security Secretary Janet Napolitano.

“The FBI is investigating it as an act of terror,” Obama said in a brief appearance before reporters after that session, because that word applies when innocent civilians are targeted with bombs. But he said the government doesn’t know whether the attack was the work of a “malevolent individual” or a foreign or domestic organization.

Once the alleged perpetrators are identified and a motive becomes apparent, Washington’s rhetorical attention will be turned to those developments for several more days. So if there’s a break in the case soon, any advancing of the president’s top domestic policy initiatives will be delayed to next week or maybe beyond.

The Capitol Police intensified security checks at entrances, including deploying extra bomb-sniffing dogs to greet visitors, but said they were acting out of abundance of caution and not because of any specific threat.

Obama’s first comments on Monday evening about the deadly attack were notable in part because he did not then use the words “terror” or “terrorism,” even though by then the FBI was running the federal investigation through its Joint Terrorism Task Force.

But several senior members of Congress didn’t hesitate to use the word, because they said it should be applied to this sort of attack whether it was planned by American citizens or was the work of foreigners.

Senate Intelligence Chairwoman Dianne Feinstein, D-Calif., said the briefings from the White House left no doubt that the incident was terrorism, though the nature of the perpetrators was not known.

“It was coordinated, there were multiple explosions, you had someone who was able to penetrate security,” said Peter T. King, R-N.Y, a senior member of the House Homeland Security Committee.

“Amateurs don’t do that, so this was well-planned and coordinated. It’s a terrorist attack, it’s a question of who did it,” said King, who volunteered on MSNBC that no mention of the marathon was made in either of two briefings he received on potential threats last week. “We have to consider if it was Islamic jihad; it could also be white supremacists, anti-government people — all of that is being looked at right now.”

House Homeland Security Chairman Michael McCaul, R-Texas, said the attack had “all the hallmarks of a terrorist attack,” and said he was especially worried about the nature of the shrapnel apparently in the devices. “If ball bearings were used and it is an IED device, that’s very traditional, classic, what we’ve seen overseas in Afghanistan and Iraq, and the threat that we’ve been very concerned about entering into the United States, and something that’s very easy to pull off,” he said.