The fate of President-elect Donald Trump’s Cabinet is still unclear after Republican senators spent much of December carefully dodging questions about Robert F. Kennedy Jr. ’s views on vaccines, accusations of sexual misconduct against Pete Hegseth and Tulsi Gabbard’s 2017 meeting with then-President Bashar Assad of Syria.

While some GOP senators have indicated they are all-in for Trump’s picks, others have withheld support, for now, especially on some of his more controversial nominees. The dynamic is injecting uncertainty into the process as Republicans prepare to take the Senate majority in January with a four-seat margin and as Trump aggressively challenges them to confirm his Cabinet immediately.

It’s not unusual for senators to wait until after confirmation hearings to publicly announce a decision. But Republicans are under more pressure than usual as Trump and his allies make clear that they will confront senators who don’t fall in line.

“You only have control of the Senate because of Donald Trump,” the president-elect’s son, Donald Trump Jr., warned during a media appearance this month. “Without that, you’d be relegated to insignificance.”

There has been one casualty of the process so far — former Rep. Matt Gaetz of Florida, who withdrew from contention as attorney general after senators relayed private concerns. But Trump has enthusiastically stood by the rest, including Kennedy for secretary of Health and Human Services, Hegseth for secretary of Defense and Gabbard for director of national intelligence.

With hearings starting by mid-January, before Trump is even inaugurated, senators will soon have to decide how closely they will scrutinize the nominees and whether they are willing to vote against any of them. Republicans will have a 53-47 majority, so Trump cannot lose more than three votes on any nomination if Democrats are united in opposition.

The outcome of the confirmation process, and the level of dissent in the Senate, will likely set the tone for Trump’s presidency and his relationship with Congress, which was frequently tumultuous during his first term. He often clashed with the Senate, in particular, but has signaled he expects Republican senators to be more compliant this time around.

“It’s not about putting yeses on the board, it’s about keeping nos off the board,” said Oklahoma Sen. Markwayne Mullin, one of Trump’s top allies in the Senate, who speaks with him frequently.

While most Senate Republicans have scrambled to display as much loyalty to Trump as possible, a handful have made clear that they are willing to defend the body’s “advise and consent” role. Among the senators to watch are moderate Republicans Lisa Murkowski of Alaska, Susan Collins of Maine and incoming freshman Sen. John Curtis of Utah.

“Anybody who wants to give me heat for doing my job, bring it on,” Curtis said Sunday on ABC’s “This Week” when asked about vetting Trump’s nominees. “This is my job. It’s my constitutional responsibility.”

Still, even moderate senators have shied away from directly criticizing Trump’s picks. And not a single Republican has gone on the record against a nominee.

Several of Trump’s picks are expected to sail to confirmation, perhaps even with some Democratic votes. Sen. John Fetterman, D-Pa., has indicated he will support Florida Sen. Marco Rubio for secretary of State and Rep. Elise Stefanik for United Nations ambassador, as have a few other Democrats.

For the more controversial nominees, though, party unity will be key.

One of Trump’s most embattled picks is Hegseth, a Fox News host and veteran who some see as inexperienced and has publicly questioned whether women should serve in combat. He has also faced allegations of sexual assault and excessive drinking that he has denied. But it’s all given some senators pause, despite Trump’s enthusiastic support.

Hegseth has faced particular pressure from Iowa Sen. Joni Ernst, herself a combat veteran who has worked to address sexual assault in the military. She has met with Hegseth several times, and has not yet said she will support him. She will have a chance to question him, publicly and face-to-face, in a Senate Armed Services Committee confirmation hearing that is scheduled for Jan. 14.

Though a hearing for Gabbard has not yet been set, senators will also be able to question her publicly and in a classified setting about her trip to Syria after the U.S had severed diplomatic relations. Gabbard has defended the trip, saying it’s important to open dialogue, but critics hear echoes of Russia-fueled talking points in her commentary. Assad fled to Moscow earlier this month after opposition forces overtook Syria in a surprise attack, ending his family’s five decades of rule.

While Republican senators have mostly refrained from publicly expressing concerns about Gabbard’s ties abroad, nearly 100 former senior U.S. diplomats and intelligence and national security officials have urged Senate leaders to schedule closed-door hearings to allow a full review of the government’s files on her.

Senators have been a bit more openly skeptical of Kennedy, who has long questioned the use of some vaccines.

After a report in the New York Times that one of his advisers filed a petition to revoke approval for the polio vaccine in 2022, Senate Republican leader Mitch McConnell issued a statement saying that “efforts to undermine public confidence in proven cures are not just uninformed — they’re dangerous,” and that “anyone seeking the Senate’s consent to serve in the incoming administration would do well to steer clear of even the appearance of association with such efforts.”

McConnell, who had polio as a child, is leaving leadership next year but will stay in the Senate. His votes will also be closely watched after years of tension with Trump as he assumes a new role free from the responsibilities of leadership.

Like McConnell, many senators have taken an “advice” approach, telling the nominees what they need to do to be confirmed.

North Carolina Sen. Thom Tillis says he’s told all of the nominees he’s met with so far, “go out and see what the press is saying about you, find your top 10 and disarm the conversation by having a good solution for why that isn’t you.”

In addition, Tillis said, “you’ve got to have a good showing in committee.”