Washington (CNN) Capitol Hill was abuzz this week as the first of President-elect Donald Trump's Cabinet nominees went through a gauntlet of confirmation hearings.

While the nominees are mostly on track to be confirmed in the Senate, where the Republicans have a 52-48 edge, there were some moments that stood out.

From nominees diverging with Trump to senators seeking assurances that Trump's Cabinet would check his impulses to Democrats pulling out all the stops in mostly futile efforts to derail them, here are some of the top moments from the week's hearings.

Tillerson doesn't win over skeptics

After this week, the nominee in the most jeopardy of failing to secure confirmation is Trump's choice for secretary of state, former ExxonMobil CEO Rex Tillerson.

A handful of Republican senators, including Florida Sen. Marco Rubio and South Carolina Sen. Lindsey Graham, say they have not made up their minds on supporting him after an at-times rocky confirmation hearing.

Rubio was Tillerson's toughest interlocutor, grilling him on a slew of questions about human rights and expressing displeasure when the businessman refused to denounce the behavior of Russia, China, Saudi Arabia and the Philippines.

Rubio alone could hold up Tillerson's confirmation, as he is part of a one-vote majority of Republicans the Senate Foreign Relations Committee, though the Senate could technically hold a vote even if Tillerson stalls in committee.

The former Trump rival stressed the importance of "moral clarity" in US foreign policy and was unsatisfied with Tillerson's answers. "When the world sees that "the United States is not prepared to stand up and say, yes, Vladimir Putin is a war criminal, Saudi Arabia violates human rights, it demoralizes these people all over the world," he said.

In another exchange that set off senators, Tillerson said a conversation with Trump about Russia "has not yet occurred," saying they've only discussed world affairs in general terms.

JUST WATCHED Tillerson claims no talks of Russia with Trump Replay More Videos ... MUST WATCH Tillerson claims no talks of Russia with Trump 00:51

But he took steps in his opening remarks to strike an overall tougher line on Moscow than Trump has to date -- an important step given bipartisan concern upon his nomination about his friendship and business relationship with Putin.

"Russia must know that we will be accountable to our commitments and those of our allies, and that Russia must be held to account for its actions," TIllerson said.

Tillerson also faced tough questioning on Exxon's lobbying against Iran sanctions.

"I have never lobbied against sanctions, personally," Tillerson said. "To my knowledge, Exxon never directly lobbied against sanctions. Not to my knowledge."

But committee Chairman Bob Corker said he recalled Tillerson calling him to lobby on the bill, and New Jersey Democrat Bob Menendez brought documents showing millions in Exxon lobbying spending into the hearing.

"There was lobbying here," Menendez told him. "It's a little amazing that you don't know Exxon was lobbying on these issues."

Kelly diverges from Trump

In another example of Trump's nominees diverging from his past stated policies, his pick to head the Department of Homeland Security showed daylight between him and Trump on some key pieces of the President-elect's agenda.

Retired Gen. John Kelly stood by US laws against the use of waterboarding and other forms of torture, doubted the efficacy of monitoring Muslims as a group in counterterrorism efforts and -- perhaps most significantly -- downplayed the importance of a physical border wall.

"A physical barrier in and of itself will not do the job. It has to be a layered defense," Kelly said, advocating the importance of partnerships with Latin American countries to combat drug and human trafficking.

Of all his campaign promises, Trump's mantra to "build the wall" has been his most enduring and least equivocal, and he has repeatedly stressed it would be a physical wall paid for by Mexico.

Trump has also called for bringing back waterboarding despite US law contravening its use and at one point called for a total prevention of foreign Muslims from entering the United States, a position that changed over time and evolved at one point to monitoring Muslims, then became a plan to have higher scrutiny on foreigners from unspecified countries with high terror activity.

"I don't think we should ever come close to crossing a line that is beyond what we as Americans would expect to follow in terms of interrogation techniques," Kelly explained as part of his answer on waterboarding and torture.

JUST WATCHED DHS pick splits with Trump's campaign promises Replay More Videos ... MUST WATCH DHS pick splits with Trump's campaign promises 02:11

Kelly agreed with questioning from Michigan Democratic Sen. Gary Peters that conducting surveillance of US mosques and creating a database of Muslims in the US raised constitutional issues.

"I don't think it's ever appropriate to focus on something like religion as the only factor (in counterterrorism)," Kelly said. "I don't agree with registering people based on ethnic or religion."

Carson asked about conflicts

Trump's potential conflicts of interest as President were the subject of the biggest flashpoint in the hearing of retired neurosurgeon Ben Carson to direct the Department of Housing and Urban Development.

Massachusetts Democrat Sen. Elizabeth Warren, one of her party's most vocal progressive advocates, pressed Carson on whether any of HUD's budget could benefit Trump or his company financially, asking him to rule it out.

"It will not be my intention to do anything to benefit any American," Carson said, getting a bit tongue-tied. "It's for all Americans, everything that we do."

Warren asked if that meant Trump could still stand to benefit from HUD projects.

"You can take it to mean that I will manage things in a way that benefits the American people," Carson said, saying he wouldn't pass up a good deal for Americans just because a small portion might benefit a particular entity.

JUST WATCHED Warren to Carson: Will HUD benefit Trump? Replay More Videos ... MUST WATCH Warren to Carson: Will HUD benefit Trump? 02:55

Democrats have repeatedly blasted Trump's decision to not place his assets in a blind trust or divest from his companies, as ethics experts say would be necessary to truly limit potential conflicts of interest from his many global financial interests. Trump laid out a plan this week of ceding control of his business to his sons that failed to satisfy his ardent critics.

Ohio Sen. Sherrod Brown took up his fellow progressive's cause, asking Carson to commit to reporting to the committee "on any issue that should arise on a property owned by Mr. Trump and his family, and any contact your subordinates receive from the Trump organization or the White House or any other source other than normal back and forth between a project and its oversight officials."

"I would be more than delighted to discuss those," Carson said, promising to work with the committee to set up a process to do so.

Mattis earns senators' esteem, with caveats

The nominee to be defense secretary, retired Marine Gen. James Mattis, earned bipartisan praise before the Senate Armed Services Committee during his hearing on Thursday.

He earned early points with the Russia hawks on the committee by diverging from Trump and talking tough on Putin.

"I've watched three presidents commit themselves to new relationships with Vladimir Putin. All three have been an abysmal failure," committee Chairman John McCain said, asking Mattis what he would do.

Mattis agreed, saying he had low expectations for cooperation with Russia and continuing to emphasize the point to the top Democrat on the committee, Sen. Jack Reed.

"I'm all for engagement, but we also have to recognize reality and what Russia is up to," Mattis said. "There's a decreasing number of areas where we can engage cooperatively and an increasing number of areas where we're going to have to confront Russia."

The topic of NATO was also raised by multiple senators. On the campaign trail, Trump indicated he may reconsider aspects of the US alliance with NATO, alarming lawmakers on both sides of the aisle.

JUST WATCHED Mattis: Trump is open to NATO conversation Replay More Videos ... MUST WATCH Mattis: Trump is open to NATO conversation 01:31

Mattis, a former supreme allied commander of NATO, voiced unequivocal support for the alliance and said he had said as much to Trump.

"NATO, from my perspective ... is the most successful military alliance certainly in modern world history, probably ever," Mattis said. "I have had discussions with him on this issue. He has shown himself open, even to the point of asking more questions and going deeper into the issue about why I feel so strongly."

But Mattis did face tough questioning about his position on women in all combat positions and gays serving openly in the military, policies now in place he had spoken against in the past. Mattis stressed that he is not looking to make changes to DoD policy, but never ruled out rolling back the decisions if it affected military readiness in his eyes.

Sessions casts himself as law enforcer

One of Democrats' top targets, Alabama Sen. Jeff Sessions, emerged from his confirmation hearings largely unscathed, facing tough questions about his past and saying that as attorney general, he would eschew the more partisan posture he has taken as a policymaker.

On question after question from Democrats about hot-button issues, Sessions emphasized that his job in the Department of Justice would be to enforce the law, not change it.

On the topic of prosecuting Hillary Clinton, a theme of Trump's campaign that he backed off after the election, Sessions pledged to recuse himself, citing potentially inflammatory comments he made on the topic on the campaign trail.

JUST WATCHED Sessions: I'd recuse myself from Clinton probe Replay More Videos ... MUST WATCH Sessions: I'd recuse myself from Clinton probe 02:00

"I believe that would be best for the country because we can never have a political dispute turn into a criminal dispute," Sessions said.

He also denied participating in the "lock her up" chants during the campaign heard at Trump rallies.

Despite past strong objections to court decisions legalizing abortion and same-sex marriage -- beliefs he still said he holds -- Sessions declared both Roe v. Wade and same-sex marriage decisions settled.

"It is the law of the land, it has been settled for some time. ... I will respect it and follow it," Sessions said of Roe.

Sessions vs. the CBC

One of the most dramatic moments in any confirmation hearing came when the nominee wasn't even in the room. Sessions' hearing stretched into a second day, where witnesses testified about his record on race.

The issue was a focal point throughout his hearings, after he failed to be confirmed for a federal judgeship in 1986 over concerns about racially-charged comments he had made and prosecutorial decisions he made -- though Republicans repeatedly defended him as a victim of character assassination.

"I deeply understand the history of civil rights and the horrendous impact that relentless and systemic discrimination and the denial of voting rights has had on our African-American brothers and sisters," Sessions said. "I have witnessed it. We must continue to move forward and never back. I understand the demands for justice and fairness made by our LGBT community. I will ensure that the statutes protecting their civil rights and their safety are full enforced. I understand the lifelong scars born by women who are victims of assault and abuse."

In the second day of testimony, New Jersey Sen. Cory Booker, civil rights legend Georgia Rep. John Lewis and Congressional Black Caucus Chairman Rep. Cedric Richmond received permission to be part of a special panel alongside African-American supporters of Sessions for what amounted to an emotional finale to the hearing.

Booker gave an impassioned plea to vote against Sessions -- the first time in history a sitting senator has testified against a fellow sitting senator in confirmation proceedings for a Cabinet position.

JUST WATCHED Cory Booker testifies against Sessions Replay More Videos ... MUST WATCH Cory Booker testifies against Sessions 02:48

"The arc of the moral universe does not just naturally curve toward justice, we must bend it," Booker said. "America needs an attorney general who is resolute and determined to bend the arc. Sen. Sessions record does not speak to that desire, intention or will."

Lewis also spoke movingly about his own history fighting with his life for equality, criticizing Sessions.

"It doesn't matter how Sen. Sessions may smile, how friendly he may be, how he may speak to you, but we need someone who's going to stand up, speak up and speak out for the people who need help, for people who have been discriminated against," Lewis said.

And Richmond slammed the committee chairman for scheduling the members of Congress last out of all the witnesses.

"To have a senator, a House member and a living civil rights legend testify at the end of all of this is the equivalent of being made to go to the back of the bus," Richmond said.

But Sessions also received emphatic support from three African-American who had worked with him throughout his career, including his former staffer on the Judiciary Committee, William Smith.

"After 20 years of knowing Sen. Sessions, I have not seen the slightest evidence of racism because it does not exist," Smith said. "I know a racist when I see one, and I have seen more than one. Sen. Sessions is not one."