Paris attack puts security at the top of the agenda two days before French election Far-right leader Marine Le Pen might capitalize on Thursday's attack.

LONDON -- Thursday’s shooting on the Champs-Elysees boulevard in Paris has pushed security to the top of the political agenda and added more unpredictability to a close presidential race two days before French voters head to the polls.

The attack, which killed one police officer, could influence voters who will cast their ballots Sunday, analysts say.

“It seems inevitable that this attack will have some impact on Sunday’s vote,” Jim Shields, professor of French politics at Aston University in Birmingham, England, told ABC News. “We have had terrorist attacks during other election campaigns but never this close to polling day.”

Four candidates lead the race, which is still too tight to call – so even a small effect on the first round of voting Sunday could make a big difference, he said.

“With four leading candidates running neck and neck and up to a third of voters still undecided, even a marginal effect in increasing support for a particular candidate could be decisive,” he said.

This could benefit two candidates, he added: far-right leader Marine Le Pen and the conservative François Fillon, who have made security and the fight against terrorism central issues in their campaigns. The candidates who could lose votes are centrist candidate Emmanuel Macron and far-left candidate Jean-Luc Mélenchon, who had seen a recent surge in polls, he said.

Le Pen, slightly behind frontrunner Macron in the polls, has already reacted to the attack by saying she will introduce tougher immigration and border control, and she will likely continue to capitalize on it, said Françoise Boucek, lecturer at the School of Politics and International Relations at Queen Mary University of London.

“I definitely think that it’s Le Pen who might try to capitalize on it the most because her agenda is really about internal security, anti-terrorism and anti-Islamism. She’s going to capitalize on this and say, ‘Look, that's what I’ve been saying all along,’” Boucek told ABC News.

France has been under a state of emergency since November 2015. The country has seen a series of attacks that have killed nearly 240 people in the past two years. Thursday’s attack reminds voters of the security challenges the country is facing, Boucek said.

“It puts internal security on the top of the agenda and on the top of people’s consciousness so I would think that this is definitely going to affect people’s decisions on Sunday,” she said.

Le Pen is expected to make it to the second round, which she is then predicted to lose to Macron, according to the polls. Boucek said she’d still be surprised if Le Pen became president, even if she does get more votes than expected before Thursday’s attack.

President Trump tweeted today that the attack "will have a big effect" on the presidential election.

The attack adds to an already unpredictable race, said Simon Lightfoot, senior lecturer in European Politics at the University of Leeds.

Thursday’s attack is likely to benefit Le Pen and Fillon, he said. Le Pen was already expected to move on to the second round so the question is whether Fillon could now get enough votes to be the second candidate.

“If it’s a runoff between two right-wing candidates; it will be quite interesting,” Lightfoot told ABC News.

But the latest polls suggest that the second-round runoff on May 7 will be between Macron and Le Pen, and even if more people vote for Le Pen because of Thursday's attack, he doesn’t think the shift will be big enough for a far-right victory.

“I don’t think it will change the runoff dramatically,” he said.

Le Pen is an anti-European Union politician who has promised to dump the euro currency. If she wins, it could change France’s place in the world and deal a blow to the E.U., already dealing with the British exit from the bloc.