Mr Santos, a 34-year-old New York Republican, has come under fierce criticism from both sides of the US political spectrum after admitting that large portions of his life story were lies - including non-existent university degrees, a made-up real estate portfolio and confusion over his religion and family history.

The growing scandal marred his first day on Capitol Hill.

Mr Santos's only respite from the posse of reporters waiting for him in the hallways was on the House floor, where he largely sat by himself. When he cast his vote to elect the House speaker, a Democratic lawmaker reportedly shouted the word "mentiroso" - the Spanish word for "liar".

Federal and state officials have now vowed to look into his finances and inconsistencies, and Brazilian authorities have pledged to re-open a long dormant fraud case against him.

None of this, however, prevents him from being sworn in as a Representative once a House speaker is elected. Top House Republicans have remained largely silent on the issue.

"There doesn't seem to be any basis for refusing to swear [him] in. He does meet the legal qualifications for members of the House," said Jonathan Entin, a constitutional law professor at Case Western Reserve University in Ohio.

Mr Santos could, in theory, be referred to the House Ethics Committee for his fabrications. That entity, however, typically reviews claims of misconduct from current members, whereas Mr Santos's lies predate his time in office.

According to Mr Entin, any criminal charge against Mr Santos might be "sufficient" for him to be expelled from the House, but doing so would require a supermajority among the majority-Republican body.

Republicans may be reluctant to remove him, as his expulsion would lead to a special election in a swing district, an unsafe bet for Republicans who hold a razor thin majority in the House.

"The politics here gets a little bit harder, especially in an age of scandal where it just seems like you can wait it out and let someone else take the news stories and the target off your back," said Casey Burgat, the director of the Legislative Affairs program at George Washington's Graduate School of Political Management.

But Republicans could eventually face a reality in which "keeping him in their conference does more harm than good for their general party reputation," he added.

An expulsion would mark a rare event in Congress: Only 20 members to date have been removed, including five in the House and 15 in the Senate, the majority of whom were expelled for being disloyal to the US at the start of the Civil War, according to the Congressional Research Service (CRS).

And whether a member can be expelled for behaviour prior to their election remains a "significant area of debate", according to CRS.

Though experts say it's unclear whether he will be kicked out, Mr Santos could likely be censured by House leadership, Mr Burgat said.

Such a move requires a simple majority and would allow Republicans to "play both sides" by avoiding booting one of their own members while still issuing a "public slap on the wrist", he said.

Mr Santos could face other consequences as well, including more lonely days on Capitol Hill.

His fabrications will likely impact his ability to maintain relationships with fellow lawmakers reluctant to engage with him in the wake of his scandals, and Republican leadership could also avoid assigning him to any significant committees.

Mr Burgat said he believes Republicans are not in a hurry to make a move on the issue as more allegations about Mr Santos's past continue to come to light.

"It seems like we haven't reached the bottom of his lying," he said.