America awoke Tuesday to images of carnage and the foreboding reality of terrorism in the homeland, which ended a run of luck and a largely peaceful 11 years since the September 11 attacks.
Constantly rolling news coverage -- showing the moment when two murderous explosions sent flames and smoke spurting into the air near the finish line of the Boston Marathon on Monday -- spooled endlessly on cable news stations.
Blood-soaked pictures stained newspaper front pages and gruesome footage of grievously wounded victims of the first successful terror bombings in more than 11 years on US soil was easily viewable on the Internet.
Meanwhile, a cycle of questioning, commentary, press conferences by law enforcement and political leaders, matched by heartrending tales of the dead, recalled the searing and unsettling days after the 9/11 attacks.
While the Boston attacks were nowhere near the scale of Al-Qaeda's airborne strikes on New York and Washington in 2001, they again debunked the idea that American soil is immune from the terrorism faced abroad.
"On 9/11, we were forever disabused of the notion that attacks like the one that rocked Boston yesterday only happen on the field of battle, or in distant countries," said the top Senate Republican, Mitch McConnell.
"With the passage of time, however, and the vigilant efforts of our military, intelligence and law enforcement professionals, I think it's safe to say that, for many, the complacency that prevailed prior to September 11th has returned."
President Barack Obama on Tuesday gave his second televised statement in as many days, even though he had few answers to share with Americans as investigators groped for a motive and culprits, be they based abroad or at home.
The politics of terrorism were already stirring.
While thousands of Americans have died on foreign battlefields and some have perished at the hand of terrorism abroad since 2001, the US home front had largely been spared mass casualty terrorism in the decade since.
Privately, political leaders have admitted there have been lucky escapes since September 11 -- and there have been incidents like the one in which a US Army psychiatrist is accused of massacring 13 people at Fort Hood in 2009.
But they admitted that it was impossible to stop 100 percent of attacks, especially after New York had a lucky escape with a foiled truck bombing in 2010.
Obama's swift appearances on television on Monday and Tuesday appeared to indicate a desire to be seen as in command of an uncertain situation.
"This was a heinous and cowardly act," Obama said at the White House. "Any time bombs are used to target innocent civilians, it is an act of terror."
The president admitted no one yet knew who is to blame but pledged to keep Americans up to speed with new developments.
Obama ran for re-election in 2012 touting his anti-terror record, killing of Osama bin Laden and fearsome crackdown against Al-Qaeda -- so if the attack did come from abroad, he may face some political liability.
He has also learned the need for presidents to appear to be in charge of national crises, notably following his uncertain response to a foiled attempt to bring down a US jetliner over Detroit in 2009.
The sense of uncertainty was compounded by an information vacuum beginning to be filled by speculation.
"Obviously, we have to, you know, consider whether it was Islamic Jihad," said New York Congressman Peter King on MSNBC.
"But it could also be white supremacists. It could be anti-government people."
With extra police deployed in New York and Washington subway systems and other precautions being taken elsewhere, political debate about how to halt such attacks was also renewed.
"It's very, very difficult to stop something like this in a free and open society," said Michael McCaul, Republican chairman of the House Homeland Security Committee.
"You really can't clamp down on security with open-air events like a marathon, like a football game, like a shopping mall," he told MSNBC.
"I don't think the American people want a 24/7 security clampdown on them. So this is a very delicate balance."
The echoes of 9/11 were not confined to politics, as even usually bitter rivals united in grief.
"NY (Hearts) B" said a message projected in light across a wall in Brooklyn on Monday night -- using the logo of Boston's Red Sox baseball franchise, which is reviled in New York.