Police said they searched the home overnight Thursday-Friday of the man they suspect killed a police officer and wounded two others before being shot dead himself on the world-famous boulevard. The risk for the main candidates was that misjudging the public mood, making an ill-perceived gesture or comment, could damage their chances.
Though Le Pen and Macron are the frontrunners, conservative candidate Fillon and far-left firebrand Jean-Luc Melenchon have closed the gap substantially in the last two weeks.
A gunman wielding a machine gun leapt out of a auto and opened fire on the Champs-Elysees, Paris's most famous boulevard, as candidates were engaging in their final TV debate ahead of Sunday's vote.
The attacker emerged from a vehicle and used an automatic weapon to shoot at officers outside a Marks & Spencer's department store at the center of the Champs-Elysees.
Far-right leader Marine Le Pen welcomed security moving to the heart of the campaign on Thursday as she took part in a prime-time interview show alongside the 10 other presidential candidates.
France's interior ministry said the gunman was killed after opening fire on the officers at around 9:00 pm (1900 GMT) on the boulevard.
More than 230 people have been killed in Islamist militant attacks in France since January 2015.
France is in a state of emergency and at its highest possible level of alert since the attacks that began in 2015.
Macron said he canceled campaign stops out of a sense of "decency" and to allow police to concentrate their resources on the attack investigation. "This fight for freedom and for the security of the French people must be the priority of the next five-year term".
Speaking in Indonesia Friday, US Vice President Mike Pence said the attack was just the latest reminder "that terrorism can strike anywhere at any time".
Following the shoot out, the Champs-Elysees was closed and authorities were telling people to avoid the area.
"It's too early to say how or whether he was connected to what happened on the Champs Elysees", ministry spokesman Pierre-Henry Brandet said.
He was shot as he walked along the street towards other policemen.
German Chancellor Angela Merkel expressed her condolences to Hollande and said her sympathy "goes out to the victims and their families", according to her spokesman Steffen Seibert.
The Islamic State group, which is being driven out of its areas of territorial control in Iraq and Syria by Western-backed coalitions and has hundreds of French-speaking fighters, claimed responsibility for Thursday's shooting via its Amaq news agency, naming the attacker as Abu Yousif al-Belgiki. But Belgium's interior minister said the pseudonym did not belong to the attacker.
For Sunday's vote, the government is mobilizing more than 50,000 police and gendarmes to protect the 70,000 polling stations, with an additional 7,000 soldiers also on patrol.
Police officials say they are now searching at least one location in the eastern Paris suburbs in relation to the attack. The attack two days ago brought it to the forefront that it is.
He vowed that, if elected, he would within weeks of taking power create a task force to coordinate French intelligence efforts against the Islamic State group.