House Speaker Mike Johnson said Wednesday that the House will set up a bipartisan task force to investigate the shooting when the House returns from recess.

"I will set up on Monday a task force, special task force within the House. The reason we'll do it that way is because it's a more precision strike, it goes quicker," Johnson told Fox News. "There is not a lot of procedural hurdles and we’ll have subpoena authority with the task force, as well. It will be compiled of Republicans and Democrats to get down to the bottom of this quickly so the American people can get the answers they deserve."

The speaker also said he will call on Secret Service Director Kim Cheatle to resign.

-ABC News’ Lauren Peller

The Department of Homeland Security’s inspector general has opened an investigation into the Secret Service’s handling of the rally.

A new bulletin listed under "ongoing projects" on the DHS Office of Inspector General website said the project objective is to "evaluate the United States Secret Service's (Secret Service) process for securing former President Trump's July 13, 2024 campaign event."

Senators will receive an unclassified, all-senator briefing via phone call Wednesday afternoon, according to Senate Majority Leader Chuck Schumer’s office.

The Secret Service, FBI and Department of Justice will address the senators.

The House will also have an unclassified, all-member virtual briefing Wednesday afternoon, multiple sources said.

Authorities suspect Thomas Matthew Crooks, the man they allege tried to assassinate former President Trump, was able to access the roof by climbing over an air conditioning unit adjacent to the building, sources tell ABC News. Though law enforcement sources say Crooks is believed to have purchased a 5-foot ladder at a Home Depot before the shooting, it does not appear to have been used to climb on the roof and was not found at the scene.

Investigators found a remote transmitter in the suspect's pocket that may have been intended to set off two suspicious devices found in the suspect's car and one in his home, according to law enforcement sources.

Devices at both locations were similarly constructed in ammunition containers using components including receivers that appear to have been paired with the remote control found in the suspect's pocket, sources said.

The receivers in each device were connected to a series of components that investigators say met the "eye test" -- having parts present that could have made viable devices, although the functionality of the devices is still being determined. The purpose of the devices is also unknown. Whether they were intended to cause a significant blast effect and hurt people or if they were designed to create smoke, fire and a low-grade blast for a diversion is unclear.

Investigators also found a tactical vest in the suspect's car, though it is unclear why he did not wear it during the assault on the former president's rally. Some investigators are wondering whether he anticipated dying in the attack.

The shooter also asked his employer if he could take a day off on Saturday but said he would return to work perhaps as soon as Sunday, the day after this attack, according to law enforcement sources. But thus far, investigators have turned up nothing to suggest that he had any accomplices or other support to carry out his deadly objective.

An examination of his phone, which the FBI has now unlocked, has not turned up any significant information about the suspect's motives -- only what sources described as "routine" information for a 20-year-old male. Thus far, investigators have turned up nothing to suggest that he had any accomplices or other support to carry out his deadly objective.

-ABC News’ Jack Date, Luke Barr, Pierre Thomas, Aaron Katersky