A day after president Donald Trump declared a national emergency - in an attempt to circumvent Congress and redirect taxpayer money to fund 230 miles of barriers along the US-Mexico border - the designation has been beset with political and legal challenges.

Democrats painted Mr Trump's declaration as evidence of a rogue president who has finally gone too far, and they vowed to stop him. While some Republicans said they supported Mr Trump, others expressed disapproval, fearing the move would set an undesired precedent or deprive other projects of necessary funds.

Even in his declaration, Mr Trump said he expected to be sued and anticipated the Supreme Court would ultimately decide the case. Still, in a freewheeling news conference on Friday, he attempted to justify the executive action in hopes of fulfilling a campaign promise that has eluded him for two years. Hours later, Mr Trump flew to Mar-a-Lago, his Florida estate, and was spotted at his West Palm Beach golf club on Saturday morning.

By Saturday, the national emergency declaration had triggered at least one protest in New York, with various groups promising to hold more across the country on Presidents' Day.

Also on Saturday, acting defence secretary Patrick Shanahan said he would soon start to examine projects that could be delayed or cancelled to free up funds for border activities.

Trump shuts down US government over Mexico border wall – in pictures Show all 15 1 /15 Trump shuts down US government over Mexico border wall – in pictures Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures The US Capitol on the first morning of a partial government shutdown in Washington EPA Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Trump shuts down US government over Mexico border wall – in pictures President Trump speaks with children who called the North American Aerospace Defense Command Santa tracker in the State Dining Room of the White House. He earlier in the day, tweeted that he was 'all alone in the White House' waiting for Democrats to make a deal on border security EPA Trump shuts down US government over Mexico border wall – in pictures Furloughed federal workers pick up free food at a pop-up store of Kraft Heinz Getty Images Trump shuts down US government over Mexico border wall – in pictures Hundreds of federal workers and contractors rally against the partial federal government shutdown Getty Trump shuts down US government over Mexico border wall – in pictures A pedestrian walk past the U.S. Capitol ahead of a possible partial government shut down in Washington, U.S., December 20, 2018. REUTERS/Joshua Roberts JOSHUA ROBERTS Reuters Trump shuts down US government over Mexico border wall – in pictures From left, House Majority Leader Steny Hoyer, Senate Minority Leader Chuck Schumer, Sen. Dick Durbin and Speaker of the House Nancy Pelosi walk to speak to reporters after meeting with President Donald Trump about border security in the Situation Room of the White House. Trump declared he could keep parts of the government shut down for "months or even years" as he and Democratic leaders failed in a second closed-door meeting to resolve his demand for billions of dollars for a border wall with Mexico Evan Vucci AP Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures A sign alerts visitors to the closure of the National Archives on the fifth day of a partial government shutdown EPA Trump shuts down US government over Mexico border wall – in pictures Hundreds of federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures Visitors read signs announcing the closure of the White House Visitor Center EPA Trump shuts down US government over Mexico border wall – in pictures President Donald Trump speaks during a round-table discussion on border security and safe communities with State, local, and community leaders in the Cabinet Room of the White House Getty Images Trump shuts down US government over Mexico border wall – in pictures A sign alerts visitors to the closure of the White House Visitor Center on the first day of a partial government shutdown EPA Trump shuts down US government over Mexico border wall – in pictures Furloughed federal workers show their IDs for entering a pop-up store of Kraft Heinz Getty Images

Speaking to reporters at the close of his first overseas tour since becoming Pentagon chief last month, Mr Shanahan said the military's Joint Staff had been conducting a "mission analysis" on ways to deal with drugs and migrants at the border. "Based on that, we can do an assessment of what would be appropriate," he said.

Mr Shanahan said the department had been preparing for weeks for a potential emergency declaration.

A defence official, speaking on the condition of anonymity to discuss internal planning, said the military's analysis included an assessment of where border barriers would be most effective in consideration of national security.

Mr Shanahan said he had leeway to determine a final figure from available funds that would be used for border-related activities - $3.6bn (£2.8bn) from designated military construction funds. He said service secretaries would be involved in identifying affected projects.

"All of this money has been assigned for different purposes, so it comes down to: What are you going to trade off?" he said.

The defence official said it was possible though unclear whether the Pentagon would devote its entire military construction pool of $3.6bn (£2.8bn) to the border.

Mr Shanahan said certain projects would not be considered, including military housing.

"We are following the law, using the rules," he said. "We're not bending the rules."

Mr Trump's announcement capped a frenetic two-month period that included the longest government shutdown in US history, at 35 days; the re-emergence of Democrats as a political force; and a Republican Party caught between taking signals from Mr Trump and bucking his unconventional impulses. It also begins a new phase of his presidency that will test the separation of powers, as he sidesteps Congress despite Republicans urging restraint.

During his 50-minute, meandering news conference in the Rose Garden, Mr Trump offered little empirical evidence to back up his assertion that there is a crisis on the border that requires an extraordinary response. Instead, he invoked hyperbolic, campaign-style rhetoric about lawlessness that he said only walls could suitably address.

"We're talking about an invasion of our country with drugs, with human traffickers, with all types of criminals and gangs," he said. He used the word "invasion" seven times.

He later said the emergency declaration was not urgent but rather expedient, as it would help him build a wall more quickly than Congress would allow.

"I could do the wall over a longer period of time," he said. "I didn't need to do this, but I'd rather do it much faster."

The legal challenges came almost immediately.

On Friday, the advocacy group Public Citizen filed a lawsuit in US District Court in Washington, seeking to block Mr Trump's declaration on behalf of three Texas landowners and an environmental group.

"We just sued Trump over his fake national emergency," the group stated. "If Trump gets away with this, there's no telling what the next concocted 'emergency' will be, who will be targeted and what emergency powers will be claimed."

Another advocacy group, Citizens for Responsibility and Ethics in Washington, sued the Department of Justice on Friday for failing to provide documents - including legal opinions and communications - related to the president's decision to declare a national emergency.

"Americans deserve to know the true basis for President Trump's unprecedented decision to enact emergency powers to pay for a border wall," the group's executive director, Noah Bookbinder, said in a statement. "The Justice Department's inadequate response raises major questions about whether even the president's own administration believes there is a legal basis for him to bypass the constitutional authority granted to Congress to appropriate funds."

On Saturday evening, the Centre for Biological Diversity, an environmental group, filed another lawsuit in federal court, saying the president has failed to identify a legal authority to take such an action, "and Congress has not enacted any emergency legislation even remotely related to border wall construction, and thus the president's reallocation of funds is unlawful."

California attorney general Xavier Becerra, a Democrat, said he planned to work with other states to take legal action against the White House. The American Civil Liberties Union said it was preparing a lawsuit for early next week, arguing Mr Trump cannot legally redirect taxpayer money during an "emergency" unless it is for military construction projects that support the armed forces.

Donald Trump declares national emergency to release funds for border wall

Mr Trump also faces political pushback, including from members of his party.

Democrats and several Republicans predicted a two-pronged response to the declaration: one, having Congress vote to reject it in the coming weeks, and two, suing Mr Trump - or at least aiding other parties that attempt to intervene.

"The president's actions clearly violate the Congress's exclusive power of the purse, which our Founders enshrined in the Constitution," House speaker Nancy Pelosi, Democratic Representative for California, and Senate minority leader Charles Schumer, the New York Democrat, said in a statement. "The Congress will defend our constitutional authorities in the Congress, in the Courts, and in the public, using every remedy available."

Most notably, Ms Pelosi and Mr Schumer said, "We call upon our Republican colleagues to join us to defend the Constitution."

Ms Pelosi's office is in the process of amassing a list of nearly 400 projects nationwide that could be jeopardised by the diversion of funds to construct a border wall, the Hill reported.

Republicans are divided over Mr Trump's declaration, with many unnerved by what they see as an executive power grab, while others are unwilling to challenge the president ahead of 2020 presidential and congressional elections.

Senator Thom Tillis, the North Carolina Republican who faces a re-election race next year, suggested it would be hypocritical for his party to support the emergency declaration after criticising President Barack Obama for "executive overreach." He warned future Democratic presidents might follow Mr Trump's precedent.

Mr Tillis described a future "president Bernie Sanders declaring a national emergency to implement the radical Green New Deal" or a "president Elizabeth Warren declaring a national emergency to shut down banks and take over the nation's financial institutions."

"I don't believe in situational principles," he said.

Other Republicans lodged an even more straightforward objection: declaring a national emergency might prompt Mr Trump to shift funds from other desperately needed projects.

Representative Mac Thornberry of Texas, the top Republican on the House Armed Services Committee, warned against tapping Defence Department and military construction accounts to build the wall.

"Doing so would have detrimental consequences for our troops," he said in a Thursday statement. "And it would undercut one of the most significant accomplishments of the last two years - beginning to repair and rebuild our military. I hope that the president will pursue other options."

Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Show all 20 1 /20 Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters yell as protesters are removed at Trump rally in Texas on February 11 Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter dressed as a border wall before the rally Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A man is restrained after assaulting members of the media including a BBC cameraman at the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump arrives for a rally in El Paso AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Trump supporters react as a couple are escorted from their seats Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter shows off a Trump doll while waiting for the rally Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Linda Padilla Dewiler, originally from Mexico, poses with a sign as Trump supporters gather to attend his rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen A supporter sports political badges on his cap Reuters Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters hold signs, one holds an Israel flag, as they cheer for the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally in front of a large "FINISH THE WALL" banner AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally as supporters hold pro-border wall signs Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen President Trump addresses the rally as supporters hold pro-border wall signs AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer during the rally AP Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer at the rally AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters cheer the president AFP/Getty Trump Texas rally: Lies, executing babies and attacks on BBC cameramen Supporters wait for the president to arrive at the rally Getty

The issue was more than a constitutional discussion for Republicans. Democrats signalled they would proceed with a privileged resolution of disapproval that would force GOP lawmakers to vote for Mr Trump's wall or oppose his emergency claim - with certain political repercussions.

By Friday afternoon, representative Joaquin Castro, D-Texas, said he had gathered more than 60 co-sponsors for the resolution.

Such a measure would pass in the Democratic-controlled House, and more than enough Republicans could break ranks to ensure its Senate passage. But Mr Trump is certain to veto the resolution, and Congress probably could not muster enough votes to override a veto.

Democratic legislative staffers huddled on Capitol Hill at 2pm on Friday, shortly after the White House issued its proclamation. According to a senior Democratic aide, no decisions have been made on how Congress will proceed with a formal measure of disapproval, but House and Senate leaders are expected to move carefully to win over as many Republicans as possible.

White House officials want to approve projects and reallocate money as quickly as possible, but no timeline has been given.

Part of their strategy is to try to use eminent domain to seize private property along the border, particularly in Texas, where they want to install parts of the barrier. Other parts of the approach are equally unclear. White House officials have not said, for example, how they plan to solicit bids on the projects or what process they will follow.

Mr Trump has long asserted that the United States is full of rapists, murderers and other violent criminals who enter illegally from Mexico, and he has pledged to address the situation by building a wall. Government data, though, shows that attempted border crossings remain near 40-year lows and that drug traffickers primarily attempt to smuggle hard narcotics through ports of entry, not through gaps between border barriers, as Mr Trump has suggested.

The biggest challenge on the border in recent years has been a surge of families seeking to cross into the United States and claim asylum, overwhelming border agents and US facilities.

White House officials plan to use $8bn (£6.2bn) to build fencing that they believe will block or discourage a wide range of immigrants.

Of that money, $1.38bn (£1.1bn) was approved by Congress on Thursday, and it can be used for 55 miles of "pedestrian fencing" in the Rio Grande Valley in Texas.

The White House plans to use $600m (£465m) from the Treasury Department's forfeiture funds account, which contains money seized by the federal government from a range of illicit activities.

An additional $2.5bn (£1.9bn) would be redirected from a Pentagon program for countering drug activities, and a final $3.6bn (£2.8bn) would be moved from military construction accounts. It is that final pot of money that White House officials said required the national emergency declaration, as the White House is generally barred from moving money from one account to another without congressional approval.

Mr Trump promised during the 2016 campaign to build a border wall and have Mexico finance it. Since becoming president, he has insisted instead that the money should come from US taxpayers.

White House officials said that more than 50 national emergencies have been declared since the 1970s, attempting to rebut concerns Mr Trump was outside his authority in taking this step.

"This is authority given to the president in law already," said acting White House chief of staff Mick Mulvaney. "It's not as if he just didn't get what he wanted, so he's waving a magic wand and taking a bunch of money."

But some presidential historians said Mr Trump's move was unusual, in part because he stopped short of describing how it would ameliorate a situation that he has not precisely defined. White House officials on Friday would not disclose where the border barriers would be placed.

Presidents have taken extraordinary steps before, at times invoking crises facing the United States. Abraham Lincoln suspended the writ of habeas corpus during the Civil War in 1861, making it easier to arrest someone without bringing the individual before a judge.

President Harry Truman tried to nationalise the steel industry in the 1950s amid tensions brought by the Korean War; he was rebuked by the Supreme Court.

Presidential scholars said Mr Trump's move on Friday, though extreme in its rhetoric, will be viewed much differently, even if he attempts to use the National Emergencies Act of 1976 to buttress his case. That is because Mr Trump is not responding to a crisis that is evident to the American people but is instead taking action after Congress rejected his funding request for the past two years.

"It shrinks the importance of Congress even more," said Douglas Brinkley, a presidential historian. "It is a wild-eyed imperial presidency."