ISIS' multipronged shooting sprees and bombings returned the horrific threat of an international terrorist rampage to a dominant place in U.S. politics that it hasn't held since the fear-filled days after September 11, 2001.
But as heavily armed police fanned out in New York City and Washington, there was none of the unity of purpose that sustained the nation after 9/11. In fact, politicians on both sides of the aisle responded by digging partisan divides even deeper as unpleasant controversies erupted over America's role in the Middle East, over who was tough enough to wage war and the plight of Syrian refugees.
It was a surreal moment in a campaign that has already been more volatile and surprising than most previous White House races.
Before this week, it's doubtful any pundit would have predicted that the front-runner for one of the major party's presidential nominations would back the idea that Muslims in the United States should be forced to register with a government database to track their movements.
But Republican Donald Trump did just that and, when asked by a reporter in Iowa on Thursday how the strategy would differ from the persecution of Jews in Nazi Germany, simply replied: "You tell me."
The billionaire real estate mogul also questioned on Fox News whether it might be necessary to close some mosques.
Trump's top rival for the GOP nomination, neurosurgeon Ben Carson, added his own inflammatory rhetoric, weighing in on the debate over whether Syrian refugees should be barred from the United States out of concerns that some are extremists.
He compared terrorists that might try to evade U.S. screening of refugees to fatally diseased dogs, injecting a new level of vitriol into a policy debate about the capacity of U.S. officials to perform background checks and screen individuals fleeing Syria's civil war.
"If there's a rabid dog running around in your neighborhood, you're probably not going to assume something good about that dog," Carson said in Alabama
on Thursday. "And you're probably going to put your children out of the way. That doesn't mean that you hate all dogs."
Earlier in the week, another leading Republican, Jeb Bush, had also poured fuel on the fire, suggesting that only Christian refugees be admitted into the country.
In a media availability in South Carolina, Bush argued, "I mean, you can prove you're a Christian ... if you can't prove it, you err on the side of caution."
The controversy over the fate of refugees was not the only spur for heated rhetoric in a week in which another Republican presidential candidate, Marco Rubio, proclaimed America was now locked in a "clash of civilization" with Islamic terrorists.
Obama hits GOP from overseas
On the other side of the aisle, President Barack Obama seemed happy enough to stoke the partisan flames, saying on Wednesday that the GOP rhetoric on the attacks was a "potent recruitment tool" for ISIS.
Two days earlier, in his first extended reaction to the Paris attacks, Obama earned unflattering reviews for a press conference in which he seemed defensive, irritated and not fully attuned to the trauma percolating back home over the attacks.
Fresh from his unfortunate declaration that ISIS was "contained" in Iraq and Syria hours before the Paris attacks last Friday, Obama testily refused to take the bait from reporters who were fishing for a mea culpa.
He conceded that the Paris attacks were "heinous" "terrible" and "sickening," but failed to deliver the kind of rallying rhetoric and bold reassurance that some Americans expect in a time of crisis.
Instead, he segued into defense of his Syria strategy that appeared at the very least off-key: "Even as we grieve with our French friends, however, we can't lose sight that there has been progress being made."
Obama then became irritated when journalists asked if he had underestimated ISIS and how he could say his strategy was working when the group had pulled off recent and bloody attacks in Beirut, Paris and on a Russian passenger airliner over Egypt.
"I just spent the last three questions answering that very question, so I don't know what more you want me to add," Obama told CNN's Jim Acosta at one point.
He also faced criticism for being willing to engage in domestic politics beyond the waters' edge, blasting Republicans for their stance on the Syrian refugees.
"At first they were worried about the press being too tough on them during debates. Now they're worried about three-year-old orphans. That doesn't sound very tough to me," the President said.
Those comments only thickened the toxicity of the political brew over the refugee debate, with Obama facing a possible veto-proof majority on legislation calling for a halt to Syrian refugee transfers into the United States.
And they provided an opening for GOP White House candidate Ted Cruz to mount a high horse after Obama's comments were widely interpreted as aimed in part at the Texas senator.
"I would encourage you, Mr. President, if you want to insult me, come back and insult me to my face," Cruz said of Obama.
"Let's have a debate on Syrian refugees right now," he added. "We can do it anywhere you want. I'd prefer it in the United States and not overseas where you're making the insults. It's easy to toss a cheap insult when no one can respond."
Kerry on Charlie Hebdo attacks
The Paris attacks also turned into a rhetorical minefield for John Kerry, who tripped up in his native tongue despite having the linguistic dexterity to deliver his condolences to France in fluent French.
The secretary of state made a distinction between the attack on the French satirical magazine Charlie Hebdo in January and the killing spree targeting cafes and a concert hall in Paris in remarks about the most recent incident.
"There was a sort of particularized focus and perhaps even a legitimacy in terms of -- not a legitimacy, but a rationale that you could attach yourself to somehow and say, 'OK, they're really angry because of this and that,'" Kerry said at the U.S. Embassy in Paris, referring to the attack on Charlie Hebdo, which had frequently lampooned Muslim extremists.
"This Friday was absolutely indiscriminate," Kerry said.
GOP presidential candidates who are portraying the administration's response to terrorism as deluded and feckless pounced.
"He needs to get some sleep and shut up," New Jersey Gov. Chris Christie said of Kerry on Fox News.
Roanoke mayor cites internment of Japanese-Americans
Another Democrat, the Roanoke, Virginia, Mayor David Bowers, also made national headlines, arguing that it would be "imprudent" to allow Syrian refugees to be located to his part of the state.
According to the Richmond Times-Dispatch newspaper, Bowers also said that the threat to America from ISIS was now "just as real and serious" as the one posed when President Franklin Roosevelt ordered the internment of Japanese-Americans in the United States after Pearl Harbor.
So surreal was the week in politics that another remarkable campaign trail development that would have been deemed unthinkable in years past passed almost without notice.
Vermont Sen. Bernie Sanders delivered a speech
at Georgetown University embracing his democratic socialist creed -- an outlier in the American political spectrum, as is seeking the nomination of a party with which one doesn't affiliate -- to put to reset questions about electability.
It's long been a truism that anyone with socialist predilections hasn't got a hope of winning the White House -- but this year's race has been marked by more unexpected turns than anticipated ones.
Another surprising aspect of a turbulent few days is that it all unfolded without any contribution from America's first family of political controversy -- the Clintons, who have lived their lives in a vortex of partisan fury.
In fact, of all the politicians tested by the Paris attacks, Hillary Clinton might have been the most sure-footed. On Monday, the former secretary of state informed her staff she wanted to lay out a comprehensive strategy on combating ISIS, sparking a furious 72-hour dash by her campaign aides to pull thoughts she had been considering for months together in a speech.
Clinton also authored a personal Tweet hitting out at Trump over the idea of database for Muslims. "This is shocking rhetoric. It should be denounced by all seeking to lead this country," Clinton wrote.
After a year hounded by controversy over her private email server, bitter feuds with Republicans, careless missteps and several tin-ear press conferences, Clinton's speech on Thursday turned out to be one of her better moments of her campaign so far.