The Department of Homeland Security Office of Inspector General is opening its third probe into the security that led to the assassination attempt of former President Trump.

In a statement Thursday, the agency said the third probe will investigate the U.S. Secret Service's planning and implementation activities for protective operations.

"Our objective is to determine the extent to which the Secret Service plans and implements protective activities to ensure the safety and security of designated protectees," the Department of Homeland Security Office of Inspector General said.

The announcement follows two prior probes into the deadly shooting at Trump's rally in Pennsylvania over the weekend.

The first, announced on Tuesday, initiated a review to examine the Secret Service's process to secure the campaign event.

The second, opened Wednesday, initiated a review of the Secret Service Counter Sniper Team's preparedness and operations.

Former President Donald Trump met with Secret Service Director Kim Cheatle to discuss the assassination attempt made against him at his Pennsylvania rally Saturday, a source told ABC News.

The meeting took place on Tuesday at the former president's hotel in Milwaukee, the source said.

This comes as Republicans are calling for Cheatle's resignation in the wake of the deadly shooting.

-ABC News' Luke Barr

Sen. Rick Scott, R-Fla., wrote a letter to President Joe Biden on Thursday demanding "absolute transparency and accountability" from his administration with the investigation into the rally shooting.

While Scott noted that he's pleased to see Congressional investigations moving forward, he said more accountability is needed.

Scott called on FBI Director Christopher Wray, Secret Service Director Kimberly Cheatle and Department of Homeland Security Secretary Alejandro Mayorkas to hold a "daily public press conference to share updates and answer questions from the American people."

Scott asked Biden if any disciplinary action will be taken against Wray, Cheatle or Mayorkas.

"Has anyone employed by the U.S. government had disciplinary action taken against them, including being placed on leave, for action or inaction connected to the assassination attempt, murder and severe injuries that occurred on July 13th?" Scott wrote.

Scott also wrote a list of 18 questions to Cheatle, which included: "If the buck stops with you, and this has clearly been established as a colossal USSS breakdown and national embarrassment of historic proportion, why haven't you resigned?"

-ABC News’ Allison Pecorin

House Judiciary Committee Chairman Jim Jordan, R-Ohio, wrote a letter to FBI Director Christopher Wray requesting more information on the Trump rally shooting -- a preview of what GOP members on the committee may ask Wray when he appears at a hearing on Wednesday, July 24.

Jordan alleges that "whistleblowers have disclosed to the Committee that the U.S. Secret Service (USSS) did not have proper resources for President Trump's campaign event in Butler, Pennsylvania because of staffing shortages due to the North Atlantic Treaty Organization (NATO) summit and First Lady Jill Biden's event in Pittsburgh."

"The information provided to this Committee raises serious questions about the thoroughness of the security planning by local, state, and federal law enforcement agencies in support of President Trump's campaign rally," Jordan said. "Law enforcement overlooked a number of vulnerabilities prior to and during the event."

-ABC News’ Lauren Peller