FILE PHOTO: Elysee senior security officer Alexandre Benalla (C) stands next to French President Emmanuel Macron during a visit to the Paris International Agricultural Show in Paris, France, February 24, 2018. REUTERS/Stephane Mahe/Pool/File Photo

PARIS (Reuters) - The former bodyguard whose violent conduct plunged French President Emmanuel Macron into his biggest political crisis this summer agreed reluctantly to face questioning by senators as their hearings resumed on Wednesday.

Alexandre Benalla, 26, is under criminal investigation after being filmed beating a May Day protester. The scandal brought the sharpest criticism Macron has faced since taking power 16 months ago, prompting the president to fire Benalla, his closest bodyguard, and shake up his office.

The prospect of Benalla’s public grilling on Sept. 19 will keep the saga in the public eye just as Macron tries to inject new life into his presidency amid a slump in popularity and economic headwinds.

Benalla had feared placing himself in legal jeopardy and only agreed to testify before the upper house’s investigating committee late on Tuesday after being told that he risked two years in prison and a 7,500 euro ($8,700) fine if he refused.

“To avoid the legal risks I am threatened with, I am forced to appear before this committee,” Benalla said in a statement.

The scandal, which was dismissed by Macron as a “storm in a teacup”, has reinforced the perception among many French people of a haughty president and undermined his claim of building an “exemplary Republic”.

A poll published by Odoxa on Tuesday had Macron’s popularity sinking 12 points between June and September, to a record low of 29 percent for his presidency. Its findings echo other surveys.

Senators from the opposition-controlled chamber resumed quizzing senior officials in Macron’s office on Wednesday.

The lower house’s own investigation, controlled by Macron’s party, was disbanded in August after opposition MPs objected to its chairwoman’s decision not to interview Macron’s chief of staff.