Representative Trey Gowdy, the oversight committee chairman, said in a letter to Pruitt that the EPA had not produced documents showing whether there was an individual waiver or authorization for purchasing first- or business-class air tickets.
The Democrats said they found no records describing specific, credible threats against Pruitt.
After taking charge of the Environmental Protection Agency, administrator Scott Pruitt reportedly wanted to change the agency's logo because it reminded him of a marijuana leaf, The New York Times reported on Wednesday.
Though Pruitt has shown no intention of relinquishing his post, and President Donald Trump has continued to voice his support, the ongoing scrutiny has influenced the administrator's travel schedule. The October memo was created by Pruitt's protective security detail, led by Pasquale Perrotta, who is known as Nino, and was used to try to justify much of Pruitt's large security detail and first-class travel.
Pruitt's aides and members of EPA's Inspector General Office have repeatedly said Pruitt faces a higher level of threats than his immediate predecessors, which has prompted round-the-clock protection and his repeated use of first-class flights since shortly after he took office last February.
But the Democrats' letter says that the assessments from the US Secret Service identify no "reports of behaviors of interest" against Pruitt, and says that "an internal EPA Intelligence Office report that disputes the administrator's claims that the nature of the threats against him justify his expenditures".
Cardi B's 'Invasion Of Privacy' Shatters Taylor Swift's Apple Music Record
Cardi was born and raised in the Bronx, New York and first came to attention for documenting her career as a stripper on social media.
If confirmed, Wheeler would be next in line if Pruitt resigns or is fired.
"This development underscores the need for the Environment and Public Works Committee to conduct effective oversight of the EPA to answer the serious questions that have come to light in recent days concerning management and ethical conduct by the administrator and his staff", Carper and Whitehouse said in a joint statement.
Politico first reported Tuesday that the career EPA security staffer who wrote the February memo, Mario Caraballo, was sacked shortly after the Democrats' account of it became public. Spokesman Jahan Wilcox declined to provide details about what specific action was taken against Carballo, the deputy associate administrator of EPA's Office of Homeland Security.
Caraballo could not be reached for comment Tuesday. Barrasso said he saw the positive impact of Pruitt's actions late last month as he and Pruitt toured a Wyoming coal mine.
Gowdy, who had led a high-profile investigation into a 2012 attack on a diplomatic compound in Benghazi, Libya, during former Secretary of State Hillary Clinton's tenure, requested documents on Pruitt's travel on February 20. Leopold told AP this week that an EPA official who responded to his request told him verbally that after checks with the agency's general counsel and inspector general's office that no such records existed.
The American Federation of Government Employees Council 238, which represents about 8,000 of the EPA's roughly 14,000 employees, has joined the boot Pruitt campaign, council president John O'Grady said in an interview Wednesday.