(WASHINGTON) — The U.S. Secret Service is taking precautions to allow former President Donald Trump to resume outdoor campaign rallies by surrounding his lectern with bulletproof glass, multiple sources told ABC News.

Normally this measure is applied only to sitting presidents, but after the first assassination attempt on a presidential candidate since Robert Kennedy in 1968, the Secret Service is making an exception.

The Secret Service declined to comment on its use of bulletproof glass. Trump’s campaign team did not immediately respond to a request for comment from ABC News.

The Secret Service recommended that Trump stop holding outdoor rallies last month after a gunman in Butler, Pennsylvania, shot him from a rooftop 400 feet from the stage, injuring his ear. A man in the crowd was killed in the attack.

Since July 13, Trump has held nearly a dozen campaign rallies, all indoors.

According to the sources, Trump privately expressed his desire to campaign outdoors and asked for assurances that security would be guaranteed.

At a rally at an indoor arena in Harrisburg, Pennsylvania, on July 31, Trump praised the size of the venue and then told the crowd, “They would have preferred us to be in an arena. I don’t know why. But we’re not going to give up the outdoor rallies. You know, all the people we had to turn away today, we can have at an outdoor rally.”

According to the sources, Trump’s bodyguard is currently preparing to surround him with glass panels on three sides – although it is not yet clear when this will happen.

“The Secret Service’s use of UpArmored glass around former President Trump is another step to ensure the campaign is and remains secure,” said Don Mihalek, a retired senior Secret Service agent and ABC News contributor. “This is not just a piece of glass, but a large, bulky and heavy piece of armored glass that requires extensive logistical capabilities normally reserved for large outdoor events.”

Typically, the armored glass is transported aboard a military transport aircraft. In Trump’s case, the Secret Service is ordering several sets to be stored across the country so they can be trucked to wherever they are needed, sources said.

Former Secret Service Director Kim Cheatle increased protection for Trump, Vice President Kamala Harris and their running mates after Butler’s shooting. Other people, such as vice presidential candidate Doug Emhoff, also received increased protection, it was reported.

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