Donald Trump signed more than 100 executive orders on his inauguration day.

It has become standard practice for new presidents to use them within hours of taking office – Joe Biden signed 17 on his first day.

They are arguably the president’s most powerful tool for enacting change – as they have the same force behind them as legislation – and bypass both Houses of Congress.

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Mr Trump’s inauguration day executive orders included declaring a national emergency at the US-Mexico border, withdrawing US birthrights from migrants’ children, and taking the US out of both the Paris Climate Agreement and the World Health Organisation.

But they do have limits – and can be subject to legal challenges.

What are they – and how do they work?

Executive orders are official instructions from the president about how US federal agencies, such as government departments and the FBI, should use their resources.

They are enshrined in the second article of the constitution, which states: “The executive power shall be vested in a president of the United States of America.”

Effectively, they are a way for the president to dictate how the federal government should be run.

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They can take various forms – from laying out major policies and requesting official reports to giving federal employees days off for public holidays.

The president’s role as commander in chief means they can also be used to control what the military does.

How quickly do they take effect?

It depends on the subject matter – and the work required to achieve the president’s aims.

Executive orders that are relatively straight forward and face no opposition can be acted upon straight away.

For example, one of Mr Trump’s latest ones pardoned all of the 6 January rioters, declaring any still behind bars in federal prisons should be released immediately.

But others that are more abstract will take longer – and require further direction on how to achieve them.

One example from Monday was the order that all agencies should “address the cost-of-living crisis”.

Those that take longer than the four-year presidential term are often overridden if a new president is elected. Many of Mr Trump’s executive orders from his first presidency were focused on undoing the work of President Barack Obama, Mr Biden’s overturned many of Mr Trump’s – and so on.

Can they be overturned?

Congress and the courts have the power to block executive orders – but this is not absolute.

For example, Congress can pass laws to override them but these can still be vetoed by the president.

Congress can also deny the required funding from being allocated.

However, Congressional opposition is less likely this time around, as the Republican Party has control of the House of Representatives, the Senate – and the White House.

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Executive orders are supposed to work within the confines of the law, which means they can also be subject to legal review.

State government officials, campaign groups, and other entities can challenge an executive order if they can prove the president is going beyond his legal powers – or the constitution.

For example, President Harry Truman was stopped from trying to seize steel mills by the Supreme Court during the Korean War after it was argued he lacked the authority to take private property without Congress’s permission.

Will Trump’s latest orders face opposition?

Many of Mr Trump’s latest executive orders are highly controversial.

Although he is less likely to face political opposition due to Republican majorities in Congress, civil rights groups and Democratic attorney generals have already signalled they will launch legal proceedings.

For example, legal action was lodged within minutes of Mr Trump officially ordering the creation of his new Department of Government Efficiency (DOGE) led by Elon Musk on Monday.

Legal action is less likely to be successful when challenging the revocation of Joe Biden’s policies – as these were lawfully approved during his administration.

Opposition groups are more likely to win against the Trump administration’s use of new, untested legal arguments, according to Sky’s US partner network NBC News.

One example is the order rescinding birthrights for children whose parents are not permanent residents or US citizens.

Birthrights – the right of citizenship to anyone born on US soil – come from the 14th amendment of the constitution, which states they apply to anyone “subject to the jurisdiction” of the United States.

Mr Trump’s executive order argues this means it does not apply to undocumented migrants – but legal experts have already indicated the language only refers to those exempt from US law – such as foreign diplomats.

Another example is Mr Trump’s proposed use of the Alien Enemies Act, which is part of the Alien and Sedition Acts 1798.

It gives the president powers to detain or deport foreign citizens during times of war – and was used during the Second World War.

However, Mr Trump’s order will likely struggle to hold up in court – as the US is currently not at war.

Rare winter storms have sparked extreme cold weather warnings – some of the first in history – for parts of the US Deep South.

Lake Charles, Louisiana, had a blizzard warning in place for the first time on record on Tuesday, local meteorologists said.

Historic snowfall of between three and six inches (eight and 15cm) was forecast across Houston, New Orleans, Alabama, and Florida, according to the National Weather Service (NWS).

And Texas was bracing itself for never-before-seen snowfall of one inch (2.5cm) per hour on Tuesday into Wednesday, the forecasters said.

Blizzards are set to bring heavy snow, sleet, and freezing rain all the way along the Gulf Coast from Texas to North Carolina – conditions usually only seen further north.

Meanwhile, Arctic air will also mean colder-than-usual winter temperatures to the US’s east coast and upper Midwest.

Residents in the Dakotas and other parts of the Midwest are being warned of the risks of hypothermia and frostbite amid forecast wind chills of between -34C and -46C.

Thousands of flights cancelled

Almost 2,000 flights were cancelled across the country on Tuesday, with around 10,000 other delays.

Both airports in Houston said they had suspended all flights in anticipation of the bad weather.

Before snow started to fall on Monday, the city’s mayor John Whitmire warned people across the state: “Get prepared to be in your house, in your residence, in your warming place for the next 48 hours.

“Don’t let even clear skies on Wednesday and other days fool you. This is a serious arctic blast.”

Meteorologist Daniel Jones said of record snowfall across the Deep South: “The last time we saw snow of this magnitude was way back in 1960.

“By modern standards this is going to be a historic and very memorable storm for this part of the world.”

States of emergency have been declared by the governors of Georgia, Louisiana, Mississippi, and Alabama, where schools and businesses were told to close.

Ten counties in New York have also put in place emergency measures.

Freezing temperatures saw inauguration proceedings in Washington DC moved inside the Capitol’s Rotunda for the start of Donald Trump’s second presidency on Monday.

Former Proud Boys leader Henry ‘Enrique’ Tarrio, who was jailed for 22 years for seditious conspiracy over the January 6 riots, has been released from prison after being pardoned by President Donald Trump.

Tarrio, who warned of a second US civil war, was handed the longest sentence for any Capitol Riots defendant for his role in planning the insurrection that sought to stop Joe Biden’s 2020 victory being certified.

Elmer Stewart Rhodes, leader of the militant Oath Keepers group, has also been freed from prison after his 18-year sentence was commuted.

President Trump has frequently referred to those jailed over January 6 as “hostages” and on his first day back in the White House, he issued a sweeping clemency order, granting pardons to more than 1,500 defendants.

Henry ‘Enrique’ Tarrio

“No quarter. Raise the black flag,” Tarrio had raged online in November 2020, angry at Mr Biden’s election win. He wanted Mr Trump to remain in office, so he and others hatched a plan, one that culminated in the storming of the Capitol.

Now Tarrio has received a full pardon from President Trump and has been released from prison.

“This marks a pivotal moment in our client’s life, and it symbolises a turning point for our nation,” Nayib Hassan said in a statement.

“We are optimistic for the future, as we now turn the page on this chapter, embracing new possibilities and opportunities.”

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Joseph Biggs, Zachary Rehl, Ethan Nordean and Dominic Pezzola

Fellow Proud Boys Biggs, Rehl and Nordean were put on trial alongside Tarrio charged with conspiring to oppose the lawful transfer of presidential power by force (seditious conspiracy) and a number of other charges in relation to January 6.

US attorney Jason McCullough said in the days after the 2020 election the defendants had started “calling for action, calling for war, if their favoured candidate was not elected”.

The prosecution revealed what they said was a secret Proud Boys internal plan entitled “1776 Returns”, an incendiary document that laid out plans to take over buildings on January 6.

Biggs, Rehl and Nordean all played leadership roles in the Proud Boys and received some of the longest prison sentences of those sentenced over the riots: Nordean with 18 years, Biggs with 17 years and Rehl getting 15 years.

Pezzola, who was accused of assaulting former Capitol Police Officer Mark Ode by stealing his riot shield and using it to smash a window at the Capitol, was sentenced to 10 years.

All four have had their sentences commuted.

Elmer Stewart Rhodes

Rhodes, the founder of the militant Oath Keepers group, was convicted of seditious conspiracy.

While he did not enter the US Capitol building, he was convicted for plotting to use force against Congress to prevent the election certification.

Prosecutors at trial showed the jury encrypted messages, recordings and surveillance videos where Rhodes spoke about the prospect of a “bloody” civil war, and warned group members they may have to “rise up in insurrection” to defeat Mr Biden if Mr Trump did not act.

The former army paratrooper, who wears an eye patch after accidentally shooting himself in the face with his own gun, was jailed for 18 years but has now had his sentence commuted.

Like Tarrio, he also has now been freed from prison.

Kelly Meggs

Meggs, an Oath Keepers “chapter leader” from Florida was convicted of seditious conspiracy and other crimes.

His wife Connie was also charged and convicted in a separate trial.

He was jailed for 12 years but had his sentence commuted by Mr Trump. His wife, like most of the January 6 defendants, received a pardon.

Kenneth Harrelson and Jessica Watkins

Oath Keepers associates Harrelson and Watkins went on trial alongside Rhodes and Kelly Meggs on criminal charges of seditious conspiracy.

While the jury acquitted them of that charge, they were convicted of a number of other crimes.

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Watkins, a transgender woman who during the trial spoke openly about the struggles she faced with her identity while serving in the military, was sentenced to eight-and-a-half years in prison, while Harrelson received four years.

Both had their sentences commuted.

Roberto Minuta, Edward Vallejo, Joseph Hackett and David Moerschel

Minuta, Vallejo, Hackett and Moerschel were a group of Oath Keepers who were put and trial and convicted of seditious conspiracy.

Their sentences – four-and-a-half years for Minuta, three years for Moerschel and Vallejo and 42 months for Hackett – were commuted by President Trump.