Everything you need to know about what the controversial president-elect can and cannot do as leader of the US.

A crucial question people around the world are asking right now is if Donald Trump will be the same in the Oval Office as he was on the campaign trail.

Many are wondering: How many of his controversial campaign promises will actually become reality?

It’s important to take a step back and look at the power of the president to see how a Trump presidency could play out.

Here’s a quick rundown:

Can Trump build a wall and make Mexico pay for it?

If Trump wants to build a wall along the entire southern border he is going to have to ask the US Congress for tens of billions of dollars.

He can’t do it without their sign-off. There has been some bipartisan talk in the past of doing more to secure the border but with a $20 trillion debt that is only going up, spending the amount it would take to build on the entire border seems like a tough sell, even with a Republican-led Congress.

He cannot – repeat – cannot make Mexico pay for it.

He said on the campaign trail that he would take remittances from the US that were being sent to Mexico. What would that even look like? Would FBI agents hang out at every Western Union and ask where the money is being sent?

If as president he signed an executive order to take people’s money, it would instantly be challenged in court.

He will be able to make sure the Supreme Court stays conservative-leaning but it’s hard to imagine any court not ruling that practice would be against the constitutional protection from illegal search and seizures.

Can Trump ban all Muslims from entering the US?

He did say he was going to “totally shut down” all Muslims from entering the United States. He later clarified that he was going to shut down people from entering who come from countries with a history of terrorism. The short answer is he can’t ban an entire religion, but there are caveats.

First let’s take a look at Americans who practise Islam. No president can keep them from entering the country. That would violate several provisions of the constitution, which guarantees freedom of religion.

READ MORE: Donald Trump – The Islamophobia president

For non-Americans it is pretty clear that he couldn’t come right out and say he was stopping Muslims from immigrating or visiting the US. The courts would probably step in if that was the case.

That doesn’t mean he can’t do it though. The president is allowed to ban people from certain countries from entering the US.

It has been done before, in 1980, when Jimmy Carter, the Democratic president, during the Iranian hostage crisis banned Iranians from entering the US unless they opposed the new government or had a medical emergency.

That means Trump can also stop the resettlement of all Syrian refugees, another one of his controversial campaign promises.

Can Trump renegotiate the Iran nuclear deal?

He can try to change what he called “the stupidest deal of all time”. He can call up the Iranian foreign ministry and say he “wants a better deal”.

There is no reason to think the Iranians would agree. As president, Trump could call the other nations who took part and ask them to put sanctions back in place in order to force the talks to resume. It seems pretty unlikely the other countries would agree to that.

He could issue new US sanctions. That seems more likely because the incoming minority leader Senator Chuck Schumer has voiced opposition to the deal.

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He could say that the limited business US companies can do with Iran is no longer allowed. It seems unlikely that other countries are going to be willing to isolate Iran again to the extent they once did.

He could sign sanctions that make it tougher for foreign companies to do business with Iran and use the US financial system. In short, he can try to make Iran renegotiate but he will likely be left with only unilateral actions.

Can Trump start a trade war with China?

Yes, on his own without Congress and no one can stop him.

He can impose harsh tariffs on Chinese goods. That will mean that everyday goods that Americans are used to being able to buy fairly inexpensively at Wal-Mart will become incredibly expensive.

That would be hugely unpopular but he has the power to do it if he wants.

Can he renegotiate the North American Free Trade Agreement, NAFTA?

He can and officials in Canada and Mexico have said they are willing to start talking. If he can he get a better deal remains an open question.

Can he force American companies to move back to the US?

No. He quite simply cannot. He can impose heavy tariffs on the products companies make in Mexico and ship to the US.

Again, US consumers would quickly feel the pain of that move.

What can Trump do in Syria?

Anything he wants. The US involvement has been done under the legal authority of the Authorization for Use of Military Force from 2001.

Congress could pass a new bill forcing him to continue to arm opposition fighters or to stop providing assistance and that would be binding, but his own party controls both chambers of Congress and are unlikely to take that step.

READ MORE: What does Trump’s victory mean for the Middle East?

Members of Congress have been reluctant to put their names to anything that authorises or stops the use of force overseas.

He can unveil his “secret” plan to stop the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS) or he can side with the Russians and stop backing the groups fighting Syrian President Bashar al-Assad and ISIL and there is little likely to stop him.

Can Trump stop “normalisation” with Cuba?

Yes. Just by signing his name on an executive order he can roll back every change President Barack Obama has made.

What can Trump do at the UN?

Anything he wants. He could try to lift sanctions on Russia over Ukraine in exchange for cooperation in Syria. Congress couldn’t stop him, but the other veto-wielding countries can.

Can he rip up the Paris climate agreement?

Yes. With an executive order everything that was mandated under the agreement would simply go away.

Can he deport undocumented migrants?

He can do that and no one can stop him – short of a congressional bill.

Can Trump make America great again?

It seems we are about to find out.

Follow Patty Culhane on Twitter: @PattyCulhane