CBS News learned that Mike Pence's chief of staff warned the Secret Service about a possible threat to him the day before the attack on the Capitol.

Marc Short called Tim Giebels on Jan. 5 to warn him about the possible threat to the vice-president. He was not specific about the nature or extent of the threat. Short had never before notified the Secret Service about a possible threat. This was based on Short's assessment that Trump would turn against Pence. The New York Times reported Short's warning to Secret Service.

Short is expected to appear before the House select Committee investigating the Jan. 6 attack as public hearings begin this month. His exact appearance date has not yet been disclosed.

Usually, the agency responsible for protecting the vice president was also the one who shared the risk assessments. CBS News learned that Short's assessment was a general one. Short did not possess evidence that he was involved in a plot. Short was aware that Trump wanted to intimidate Pence and stop the certification of the Electoral College counts. He also knew that Pence had no intention of doing this.

Short will be asked about those events when he testifies publicly. Short will likely also be questioned about his interactions with Mark Meadows, Trump's chief staffer.

According to CBS News, Meadows sent text messages to other news outlets, indicating that he was in touch with actors who helped Trump's campaign to stay in office during the period leading up to Jan. 6. Meadows was also privately assuring Mitch McConnell and other White House officials that he was asking Trump to concede the loss.

Short met with the House Select Committee on Capitol Hill in January.

Short was present with Pence at the Capitol Jan. 6, when pro-Trump rioters took over the building. The pair were forced to flee to a safe area within the Capitol compound. Trump had privately and publicly pressured Pence not to accept the results of certain election states won by Joe Biden. But, Pence released a statement stating that he couldn't.