The Senate is currently controlled by 53 Republicans, compared to 47 Democrats.
“Gaetz has a better shot at having dinner with Queen Elizabeth II than being confirmed by the senate,” Max Miller, a Trump ally and Republican, said.
He added: “I think he has a zero per cent shot of getting through the Senate… reckless pick.”
Michael Guest, the Republican head of the ethics committee, said he was “surprised” by the decision to nominate Mr Gaetz.
His committee is investigating the candidate for sex trafficking, allegations of illegal drug use, misuse of campaign funds and accepting bribes. It would be closed if Mr Gaetz resigns to become attorney general.
Other Republicans have described Mr Gaetz’s appointment as a distraction so that Mr Trump can choose another controversial, but more acceptable, candidate at a later date.
In the past, Ms Gabbard has also been on the receiving end of sharp Republican criticism for her social media posts containing pro-Kremlin narratives. She has been branded “traitorous” and accused of “parroting fake Russian propaganda”.
Trump’s secret strategy
But Mr Trump may have a strategy up his sleeve to ram through his nominations without any scrutiny.
The president-elect has demanded that the next Senate majority leader allow for recess appointments, which would allow him to unilaterally install members of his top team.
The powers to make recess appointments dates back to the era of horse-and-cart travel, when the Senate was often out of action for months at a time because of the time it took to move around the country.
To avoid key appointments being held up, the founding fathers wrote an exception into the Constitution, permitting presidents to fill vacancies during a period of recess.
George W Bush made 171 recess appointments, Bill Clinton made 139 and Barack Obama made at least 32, according to the Congressional Research Service.
The controversial tactic, which usually attracts allegations of a power grab, was not used by either Mr Trump or Mr Biden.
In 2014, the Supreme Court ruled against a number of Mr Obama’s appointments, branding them unconstitutional.
By squeezing his three controversial picks into office, Mr Trump would move a step closer to carrying out his “deep state” revenge.
The president-elect has long demonised the intelligence community, especially after it accused Russia of being behind a campaign to help him beat Hillary Clinton in 2016. Mr Trump later sided with Putin when asked if he believed his own intelligence agencies or the Russian president at a joint press conference two years later in Helsinki.
A supportive attorney general could also agree to publish the names of the Department of Justice and FBI officials behind the probe into Mr Trump’s alleged removal of confidential documents from the White House, which ended with him being charged with felonies.
It has unnerved many serving DoJ officials, who have spoken of their fears over Mr Gaetz becoming their boss in less than two months.
Dave Laufman, a former top official, said the Republican would turn the department into a “petting zoo for Trump”.
While an anonymous official, still serving in the department, told ABC News that there would be “mass resignations if he gets sworn in”.