©  AP

President-elect Trump has filled his Cabinet and a number of senior staff roles as he prepares to return to the White House in January. 

But while most Cabinet picks will likely glide through confirmation in the GOP-led Senate, several figures are sure to face intense questioning from Republicans and Democrats alike.

Defense secretary pick Pete Hegseth, Health and Human Services pick Robert F. Kennedy Jr., Director of National Intelligence pick Tulsi Gabbard and Education secretary pick Linda McMahon are all expected to face tough questioning, among others.

Attention has turned to several of the Trump picks after former Rep. Matt Gaetz (R-Fla.), who was facing allegations of sexual misconduct and illicit drug use, withdrew his name from consideration for attorney general.

One of the most contentious nominees is Army veteran and former Fox News host Pete Hegseth to head the Pentagon. 

Hegseth served in combat, but never in a command position. He has also suggested women do not belong in combat roles. 

He has also come under scrutiny for being accused of sexually assaulting a woman in 2017. Hegseth claims he "was completely cleared" and his lawyer says he settled privately to avoid the allegations impacting his career.

Sen. Susan Collins (R-Maine), talking about accusations against Gaetz and Hegseth, said “any allegation of drug use and sexual misconduct or sexual crimes are serious ones that the Senate is going to take a close look at."

Sen. Joni Ernst (R-Iowa) said “there’s a lot floating around out there ... We need to actually be able to visit with him face-to-face," adding the Senate Armed Services panel of which she's a member "will do a thorough vetting."

Ernst said a background check form the FBI on Hegseth would be “helpful.”

Trump's transition team has yet to sign a memorandum of understanding with the Justice Department to allow the FBI to conduct background checks on the president-elect's nominees, reports The Hill's Alexander Bolton.

Read more: 

• The 6 senators who could be key to Hegseth’s Pentagon confirmation

• GOP rep pushes back on Hegseth’s idea to fire ‘woke’ generals

• GOP senator: Americans don’t care about FBI background checks for Trump nominees

RFK Jr., trump's pick to lead the Department of Health and Human Services, is seen by several public officials to be unqualified, due to his lack of experience running a federal agency and unfounded theories regarding vaccines and fluoride.

He has also been accused of groping a former live-in nanny more than 20 years ago.  

The nanny, who was 23 years old at the time of the alleged assault, also claims Kennedy touched her without consent and made inappropriate advances on separate occasions. 

In October, reports indicated Kennedy and Olivia Nuzzi, then a journalist for New York Magazine, had engaged in year-long digital relationship, despite Kennedy being married. 

Kennedy has drawn attention over his views on abortion. Despite being pro-choice, he has received some early support among the GOP. Democrats are widely opposed to his nomination. 

Read more: 

• What RFK Jr. could mean for LGBTQ health care

The former World Wrestling Entertainment (WWE) executive Linda McMahon is Trump's pick to head the Department of Education. 

McMahon has been a long-time Trump ally and ran two unsuccessful Senate campaigns in Connecticut. She has no experience running a federal agency, nor has she ever been a teacher. 

McMahon and her husband Vince McMahon, along with WWE and its parent company, are facing a lawsuit that alleges the defendants failed to stop "open, rampant abuse" of young boys by a WWE employee.

McMahon's attorney has said the allegations are false. 

Former four-term Hawaii congresswoman Tulsi Gabbard rankled many members of her own party when she was a Democrat in Congress and running for the party's presidential nomination given her heterodox foreign policy views.

Now that she's a member of the GOP and appointed to be Trump's director of national intelligence, she's sure to face scrutiny from Senate Republicans as well over her past statements about Ukraine, Russia, Syria and more.

Gabbard served in the Hawaii Army National Guard and deployed to Iraq, service that several pro-Trump allies have touted to shore up GOP support.