After pulling off one of the most improbable political upsets in US history, Donald Trump has now become the country’s president-elect.

Though he will face a sharply divided nation after he is sworn in as the country’s 45th president on January 20, 2017, he immediately takes over a number of key powers enumerated to him by the US constitution, US laws, and precedent.

While the US system of government is divided among three branches – the executive, the legislative, and the judicial – intended as a structural system of checks-and-balances, Trump’s presidential power will be vastly strengthened because his fellow Republicans retained control of the two houses of the US Congress: the House of Representatives and the Senate.

Supreme Court

With two branches of government under Republican control, Trump will be looking immediately to the US Supreme Court, which has been operating a person short of its nine members since the February 2016 death of Justice Antonin Scalia.

While President Barack Obama nominated Judge Merrick Garland to replace him shortly thereafter, Republicans have refused to hold hearings on his confirmation for more than 230 days, an act of Congressional obstruction without precedent in its length (under the constitution, the Senate must confirm a president’s Supreme Court nomination).

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Garland is almost guaranteed not to receive a hearing in the next two months, and it will then fall upon Trump to nominate someone new.

His past suggestions have included staunchly conservative jurists, and if he were able to get a pick confirmed in the Senate, it would see a court split between a reliably conservative wing, a reliably liberal wing, and the swing vote of Justice Anthony Kennedy (Scalia was a reliable part of the court’s conservative wing).

The retirement or death of Justice Ruth Bader Ginsburg, the liberal stalwart who is 83, or Kennedy, who is 80, could allow Trump to significantly remake the court, with potentially major implications for issues including abortion rights, labour rights, voting rights, and more.

Legislative priorities

Among Trump’s legislative priorities are the repeal and replacement of the Affordable Care Act (the healthcare law commonly known as Obamacare), a massive programme of tax cuts, the renegotiation of trade deals, an increase in defence spending, entitlement reforms, and much more.

While it is unclear how many legislative priorities Trump would be able to enact, Congressional Republican majorities make it much easier for him.

However, Democrats still retain a potent trump card on Trump with the Senate filibuster tactic, which means on legislation they choose to prevent voting on through unending floor debate, Republicans would have to reach a threshold of 60 votes to pass a bill, which is more than the 51 Senate votes they will now have.

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But even then, Republicans have other parliamentary tactics available to them that could see them minimise Democratic opposition methods.

For one, they could eliminate the filibuster altogether, a process that former Democratic Senate Majority Leader Harry Reid took small steps to begin when he changed Senate rules to restrict filibustering in some judicial appointments (excluding the Supreme Court).

Congressional Republicans can also do an end round outside of the filibuster altogether in a process known as budget reconciliation, which Republican House Speaker Paul Ryan has suggested he would embrace to enact wide-ranging legislative goals including a massive reduction in government programmes and social safety nets.

All of that together creates a context for Trump similar to the great power Obama wielded in his first two years in office, when he signed Obamacare, a massive government stimulus spending programme, and the watershed Dodd-Frank financial reform bill.

All of those things are now at risk of being overturned or extensively altered by a Trump administration, at least until mid-term elections are held in 2018, which often favours the party out of power.

Executive orders

Because Obama only had Congressional majorities for his first two years in office, the rates of legislation his administration wanted passed slowed down significantly in his remaining six years.

As a result, many of Obama’s achievements were either in the realm of foreign policy, where presidents are given more legal latitude to operate independently of Congress, or through so-called executive orders, whereby a president uses his or her discretion to execute or enact existing legislation.

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Executive orders have been standard practice embraced by presidents from both parties over the years, but many Republican critics of Obama, including Trump, have decried his use of them, and courts sometimes have ruled that certain executive orders exceeded their legal authority.

On day one of a Trump presidency, he would be able to begin the process of unwinding any number of Obama’s orders, including: mandating higher emissions standards; shielding children of illegal immigrants from deportation; giving higher wages for government contractors; and outlawing the use of torture by US intelligence officials.

According to a New Yorker interview in September with one of Trump’s key advisers, Stephen Moore, Trump’s team is aiming for a “First Day Project”.

As Moore said: “Trump spends several hours signing papers – and erases the Obama presidency”.

He added: “We want to identify maybe 25 executive orders that Trump could sign literally the first day in office”.

In addition to overturning executive orders, a Trump administration could also put at risk several of Obama’s signature agreements he negotiated on behalf of the US as commander-in-chief.

Among these deals are the landmark nuclear non-proliferation deal negotiated between Iran, the US, and six world powers, and the historic global climate accord signed in Paris in December 2015.

Trump has decried both policies and vowed to cancel both agreements, something consistent with a president’s power in foreign affairs.

Trump has also decried international alliances such as NATO, and suggested he might instruct the government to stop paying UN dues.