President-Elect Donald Trump has announced over half of his Cabinet nominees, many of whom have been criticized by Democrats and even by some Republicans.

Those on the left have expressed outrage at a few of Trump’s choices like Jeff Sessions, who has in the past been accused of racism, and Michael Flynn, who has said that it’s logical to be afraid of Muslims. Still other Cabinet selections have pleased establishment Republicans who worried that Trump’s picks might be entirely unconventional. For example, Trump recently named Tom Price, an Obamacare critic, as his secretary of health and human services, a decision met with praise from members of the Republican party.

But could any of Donald Trump’s nominees be rejected by the Senate? What is the confirmation process like, and what sort of problems might these nominees experience? Here’s everything you need to know about Donald Trump’s cabinet appointments and the process of getting them into office.

1. Republicans Only Need a Simple Majority to Approve a Nominee

It will be relatively easy to get most of Donald Trump’s appointments through the Senate, and it’s all thanks to Democrats.

In the past, it was possible to block a cabinet nominee with the use of a filibuster, at which point a three-fifths majority would be required. However, this procedure was ended by the Democrats during the 113th Congress. Now, only a simple majority is required in order to get a cabinet nominee confirmed.

Trump just needs 51 votes for each nominee, then, and in most cases that shouldn’t be a problem. Starting in 2017, the Senate will consist of 52 Republican seats (or 51 depending on the results of the Louisiana runoff election). So as long as the entire Republican party is behind a nominee, that person will be approved.

Democrats can make the nominating process difficult by holding several days of hearings and going through each pick’s controversial past. In fact, several Democrats told Politico that they don’t plan to fast-track any of Trump’s picks, particularly after the way Republicans treated Supreme Court nominee Merrick Garland.

“They’ve been rewarded for stealing a Supreme Court justice. We’re going to help them confirm their nominees, many of whom are disqualified?” Democratic Senator Sherrod Brown told Politico. “It’s not obstruction, it’s not partisan, it’s just a duty to find out what they’d do in these jobs.”

2. Jeff Sessions & Steven Mnuchin Will Face Tough Hearings

Two of Donald Trump’s cabinet picks will face quite a bit of scrutiny from Democrats during the nominating process.

The first is Jeff Sessions, the nominee for attorney general. Sessions has come under fire for past accusations of racism; in 1986, he was nominated to be a judge on the U.S. District Court for the Southern District of Alabama, but he was not approved when old comments of his came to light, such as when he allegedly said that he was okay with the Ku Klux Klan until he found out they smoked pot.

All eight Democrats on the Judiciary Committee recently signed a letter saying they want to hold several days of hearings on Jeff Sessions, specifically going through his history with civil rights.

“There’s no presumption on my part that anyone nominated is going to make it through very, very quickly. They have to prove their mettle before the committee,” Dick Durbin, the second-ranking Democrat in the Senate, told Real Clear Politics. “There are a lot of contradictions here between the people he’s named, their backgrounds, their philosophies, and what he said in the campaign. Expect to hear more.”

But while Democrats have decried Sessions’ nomination, there is little evidence that any Republicans plan to oppose his appointment. It certainly helps that Sessions is himself a senator, and members of the Senate tend to be easily approved.

“I look forward to the Senate’s fair and expeditious treatment of our colleague’s forthcoming nomination, just as it promptly processed President Obama’s first Attorney General nomination, which concluded with a timely up or down vote,” Senate Majority Leader Mitch McConnell said in a statement.

Some Democrats, including Joe Manchin of West Virginia, have even expressed support for Sessions, which all but guarantees that he will be approved. For Sessions to be rejected, every single Democrat in the Senate would need to vote him down, and then they would need to convince Republicans to reject him as well. There is no evidence that this will happen at this time.

If there’s anyone Democrats could theoretically prevent from being nominated, it’s the second controversial pick, Steve Mnuchin, Trump’s choice for treasury secretary. Mnuchin is a veteran of Goldman Sachs, which has sent Democrats into a tizzy but has also disappointed many of Trump’s supporters, who disliked Hillary Clinton because they felt she was being influenced by Wall Street.

At this time, no Republicans have publicly opposed Mnuchin. But the 53-year-old banker will almost certainly face some difficult questions during his hearings, particularly as the bank he worked for, OneWest Bank, was recently accused by two nonprofits of discriminatory practices towards minorities, according to The USA Today. And with such an anti-Wall Street sentiment dominating both sides of the political debate recently, and with Mnuchin having no relationship with those in the Senate, it certainly would not be shocking to see a few Republicans going against him.

Wilbur Ross, Trump’s pick for secretary of commerce, is also a former investment banker, although he never worked for Goldman Sachs and does not have nearly as controversial a past as Mnuchin.

3. James Mattis is Technically Not Eligible to Be Secretary of Defense

James ‘Mad Dog’ Mattis will be Donald Trump’s nominee for secretary of defense. Mattis is a retired United States Marine Corps general who is almost universally beloved among his colleagues, and under normal circumstances he would likely face no issues being approved.

But the problem is that Mattis isn’t technically eligible for the job. That’s because federal law requires the secretary of defense be someone who has not served in active duty in the past seven years. Mattis only retired three years ago, so he does not meet that standard.

In order for Mattis to be appointed, Congress must waive this requirement, and there is precedent for doing so. In 1950, Congress signed a waiver to allow George C. Marshall to become secretary of defense, as he retired just two years before being nominated for secretary of defense.

Some Democrats in recent days have said that they will oppose the effort to waive the seven-year requirement. Because any senator can call for a 60-vote threshold for the passage of legislation, Democrats could block Mattis’ nomination if they all vote to reject the waiver. And New York Senator Kirsten Gillibrand recently said she will do exactly that.

4. Trump’s Secretary of State Pick Could Face Republican Opposition

Although Trump has not yet announced his secretary of state pick, he is reportedly down to four names, two of whom have already faced Republican opposition.

One of those is John Bolton, who served as U.S. ambassador to the United Nations during the George W. Bush administration. This would be a surprising choice considering that Bolton is one of the architects of the Iraq war, which Trump repeatedly called a disaster during his campaign. Because of Bolton’s foreign policy history, Republican Senator Rand Paul of Kentucky recently said that he would do absolutely everything he can to block Bolton if he’s nominated.

“He’s opposed to everything Donald Trump ran on: that the Iraq war was a mistake, regime change made us less safe in the Middle East, including in Iraq…I don’t know how a President Trump could appoint someone who’s diametrically opposed to everything Donald Trump ran on,” Paul said, according to Politico.

Paul didn’t rule out a potential filibuster, although the Senate would just need 51 votes to break that. The senator from Kentucky cannot unilaterally block Bolton’s nomination, but if the entire Democratic party opposes Bolton, only one more Republican vote in addition to Paul’s would be necessary in order to reject him.

Another potential secretary of state is Rudy Giuliani, the former mayor of New York City. Rand Paul has said he would also oppose Giuliani, saying that Giuliani has a streak of being in favor of foreign intervention.

“If you look at Giuliani’s statements, you will find he has advocated bombing Iran, he has advocated for intervention, to my knowledge he’s never admitted the Iraq war was a mistake,” Paul said. “To me, a big part of what Donald Trump said, in hundreds of speeches, was that the Iraq war was a mistake. I don’t know how you could appoint someone to be in charge of the Department of State who believes the Iraq war was a benefit.”

Trump’s third potential secretary of state nominee is David Petraeus, who Rand Paul has said he has a problem with too. Petraeus’ hearings will almost certainly focus on the fact that in 2015, he plead guilty to sharing classified material with a biographer; he received a $100,000 fine and two years’ probation, which has not yet ended.

The fourth potential secretary of state pick is Mitt Romney, who would likely sail through his confirmation hearing without any issues.

5. Nikki Haley, Tom Price, Elaine Chao and Betsy DeVos Are Likely Locks

Outside of the names mentioned above, most of Trump’s other cabinet picks should likely have no issue getting through the appointment process.

Reince Preibus, the White House Chief of Staff nominee, is also the chairman of the Republican National Committee, and so it would be shocking if a single Republican did not vote in his favor. Nikki Haley, Ambassador to the United Nations, is also very popular among members of her own party and across the aisle as well. Ben Carson’s qualifications for the role of secretary of Housing and Urban Development have been called into question, but no Republicans have yet spoken out against his nomination.

The remaining cabinet nominees are Tom Price, Elaine Chao, and Betsy DeVos, all of whom have been met with overwhelming praise from Republicans, particularly some establishment Republicans who opposed Donald Trump’s nomination.

Jeb Bush, for example, was enthusiastic about the selection of Betsy DeVos for secretary of education.

“She has a long and distinguished history championing the right of all parents to choose schools that best ensure their children’s success,” Bush said on Facebook. “She has a long and distinguished history championing the right of all parents to choose schools that best ensure their children’s success.”

Trump has yet to name his nominee for the following positions: Secretary of State, Secretary of the Interior, Secretary of Agriculture, Secretary of Labor, Secretary of Energy, Secretary of Veterans Affairs, Secretary of Homeland Security, Administrator of the Environmental Protection Agency, United States Trade Representative, Director of the Office of Management and Budget, Chairman of the Council of Economic Advisers, and Administrator of the Small Business Administration.