U.S. President Donald Trump waded into France’s presidential election on Friday, tweeting that he expected the killing of a policeman in central Paris to have an impact on Sunday’s vote.

Islamic State claimed responsibility for the fatal shooting late on Thursday of a French policeman on the Champs Elysees by a French national who lived in Paris.

“Another terrorist attack in Paris. The people of France will not take much more of this. Will have a big effect on presidential election!” Trump said on Twitter.

In an interview with The Associated Press, Trump said he thought the attack would “probably help” Le Pen. While both Trump and the White House made it clear that he was not endorsing Le Pen, he told the AP she would be “the candidate who is “strongest on borders, and she’s the strongest on what’s been going on in France.”

The attack prompted far-right presidential candidate Marine Le Pen to say on Friday that France should reinstate border checks and expel foreigners who are on the watch lists of intelligence services.

Le Pen, who has campaigned on an anti-European Union, anti-immigration platform, was the only major French candidate who backed Republican Trump in the Nov. 8 U.S. presidential election.

Trump ran for the White House on a pledge to get tough on immigration and his administration has imposed restrictions including a controversial ban, stalled in U.S. courts, on travelers from Muslim majority nations.

In his election campaign, Trump seized on the last year’s Brexit vote in the United Kingdom as an example of disillusioned voters rising up against the political establishment and forged a friendship with Nigel Farage, a leading campaigner for Britain’s withdrawal from the EU.

On Thursday, former U.S. President Barack Obama spoke with a different French candidate, Emmanuel Macron, a pro-EU centrist.

Macron is leading most opinion polls for the election’s first round on Sunday and is expected to contest a second-round run-off with Le Pen. Obama’s spokesman said the former U.S. president, who is popular in France, was not making a formal endorsement.