President-elect Donald Trump is poised to kick off his second term by sending the Senate an unconventional slate of nominees for powerful executive branch positions, seeing his 2024 victory as validation of a voter desire for disruption. But how much disruption will America’s “cooling saucer” tolerate? The soon-to-be Republican-led chamber is already showing it has its limits by effectively sinking Trump’s choice of far-right former Rep. Matt Gaetz, R-Fla., for attorney general amid allegations of sexual misconduct and concerns about his qualifications. The Senate will be split between 53 Republicans and 47 Democrats in the new session, meaning Republicans can lose no more than three votes to confirm nominees without requiring some bipartisan support. A 50-50 tie can be broken by Vice President-elect JD Vance. Here are nine key senators to watch in the nomination battles. Sen. Susan Collins, R-Maine The five-term centrist Republican is the sole remaining Republican senator representing a blue state. She has survived politically due to her willingness to buck her party at times, such as her vote to convict Trump on impeachment charges of inciting an insurrection on Jan. 6, 2021. Collins intends to run for re-election in 2026 in a state that Trump just lost by 7 points, meaning she’s certain to be a top Democratic target. Trump’s cabinet picks present an opening for Collins to demonstrate her independent streak if she chooses to vote against some of his more controversial or radical picks. An added dynamic for Collins: She’s about to become the chair of the powerful Appropriations Committee. That gives her an opportunity to cut bipartisan deals on government spending bills, but it could also deepen her allegiance to the party that’s elevating her to that coveted role. Sen. Lisa Murkowski, R-Alaska A member of an endangered species known as moderate Republicans, Murkowski is set to wield a significant amount of power during Senate votes on some of Trump’s more controversial policies and nominees. Murkowski has already shown she will be outspoken in her opposition to Trump’s picks for his cabinet, telling reporters of the Gaetz pick, “I don’t think it’s a serious nomination for the attorney general. That’s Lisa Murkowski’s view.” Murkowski is also a rare Republican who supports bringing back the abortion-right protections included in Roe v. Wade, which could play a role in her votes on health care-related personnel and a potential new Supreme Court vacancy. And she isn’t up for re-election in deep-red Alaska until 2028. Sen. John Thune, R-S.D. The incoming majority leader is nobody’s idea of an ultra-MAGA Republican, but he understands his assignment: advance the Trump agenda. Thune will have to balance that with the institutionalist instincts that have earned him respect on both sides of the aisle. The nominations will be the first big test of his leadership style. Where does he defer to Trump? Where does he draw the line? Does he choose to be a heat shield for members who quietly want to buck Trump without doing so publicly? And how does he manage his relationship with Trump? The answers will set the tone for a long-awaited new era facing the Senate GOP. Sen. Mitch McConnell, R-Ky. McConnell is the ultimate free agent as he relinquishes the job of Senate Republican leader after a record 18 years. His quarrels and disagreements with Trump are well-documented. As GOP leader, McConnell’s style was usually to read the political winds within his party and follow them. Now, he doesn’t have to. He turns 83 in a few months and has two more years on his Senate term. The cabinet nominees could be an opportunity to flex his muscle and use his vote to shape Trump’s agenda. Will McConnell use his clout and reservoir of goodwill within the caucus to say no to some Trump picks? Or will he err on the side of acquiescence to the MAGA leader’s wishes? He’s offered one hint so far: Though he didn’t say anything publicly, McConnell was one of at least five Republican senators, including Collins and Murkowski, who privately made clear that they would oppose Gaetz for AG. McConnell is an outspoken Russia hawk who favors NATO and the post-World War II order and has signaled that he plans to use the coming years to battle the isolationist forces that have found a home in Trump’s “America First” agenda. As one example, how will he respond to the Russia-sympathetic views of former Rep. Tulsi Gabbard, Trump’s pick for director of national intelligence? Sen. Thom Tillis, R-N.C. Tillis faces re-election in 2026 after winning his first two elections by less than 2 points. He’ll undoubtedly be a Democratic target in an election year where they have few Senate pickup opportunities. North Carolina is a tricky state even for a Republican — he’ll need to be renominated by a GOP base that can be attracted to far-right figures and balance that with appealing to a general electorate in the purple state. How closely does Tillis stick to Trump in a cycle where, unlike in 2020, the president-elect won’t be on the ballot to give him coattails? The nominations will provide a clue. Sen. Bill Cassidy, R-La. Heading into a Trump presidency, Cassidy is expected to be front-and-center as the Chairman of the Health, Education, Labor and Pensions Committee. His committee is expected to look into Robert F. Kennedy Jr.’s nomination as the Health and Human Services Secretary (though the Senate Finance Committee will be tasked with reporting the nomination to the full Senate). And Cassidy, a physician himself, has kept his cards close on how he feels about the vaccine-skeptic. As HELP chairman, Cassidy will also be knee-deep in any discussions about the future of health care policy, including Medicare and Medicaid. He’s up for re-election in 2026, and his vote to convict Trump in his impeachment trial for inciting an insurrection, as well as any feud over nominees, could play a part in whether Trump chooses to support Cassidy or a potential primary challenger. Sen.-elect John Curtis, R-Utah Stepping into the seat vacated by outgoing Sen. Mitt Romney, R-Utah, many are wondering whether Curtis will be more like the institutionalist senator he is replacing, or fellow Utah GOP Sen. Mike Lee, a hard-right figure who has become a Trump ally. The answer may be something in the middle. “He is not Mitt Romney and he is not Donald Trump. He’s got his own brand and he was very clear about that in his primary and his general election,” former GOP Rep. Carlos Curbelo of Florida told NBC News recently. Speaking during his primary debate in June, Curtis said of Trump, “I’m not going to give him an unconditional yes to anything that he wants.” Curtis has already made his presence known by joining the private reesistance to Gaetz. But Gaetz was just the first real test for Senate Republicans in a second Trump presidency, raising the question: Will Curtis be the same kind of check on Trump that Romney was on both nominees and policy? Sen. John Fetterman, D-Pa. Fetterman has made a name for himself in the halls of the Capitol for his brash, unfiltered way of communicating (and the way he dresses). But Fetterman has also carved out a unique identity by breaking with his party’s left — through his unrelenting support of Israel despite the civilian casualties caused by its military campaign in Gaza and his remark that Democrats “lost ourselves” when it came to key issues like immigration. In a party that’s currently doing some soul-searching, Fetterman’s voice could play a major role in that conversation for Democrats. And has expressed a willingness to support some of Trump’s picks for Cabinet jobs, including for his former 2022 rival, Mehmet Oz, to run Medicare and Medicaid. “He’s going to pick people that are going to disagree with me, and they’re never going to be my first choice,” Fetterman told NBC News. “So that’s kind of how democracy tends to work. … I’m not going to be part of the collective freakouts.” Sen. Jon Ossoff, D-Ga. Ossoff faces re-election in 2026 in a state where Trump just snapped a Democratic winning streak that dates back to the first-term senator’s 2020 election win. He’ll probably be a top GOP target for defeat next cycle. The executive nominations could provide him some opportunities to show bipartisan bona fides, at least when it comes to Trump’s more mainstream picks. The confirmation battles will also provide some early hints as to how Ossoff is planning to position himself ahead of an undoubtedly difficult re-election bid in Georgia, where Democrats will seek to prove that their victories in 2020 and 2022 were not a fluke. This story first appeared on NBCNews.com. More from NBC News: Senator introduces bill to compel more transparency from AI developers Top federal prosecutor in New York announces resignation GOP senator argues Americans ‘don’t care’ who conducts background checks for Trump Cabinet picks