In a damning statement, California Attorney General Xavier Becerra said the president “treats the rule of law with utter contempt” and he will “likely lose this case in court”.
In television interviews on Sunday and Monday, Becerra said the lawsuit would use Trump’s own words against him as evidence that there was no national emergency to declare.
In sum, President Trump is being accused of acting illegally and using his executive powers to push ahead with a pet project many are opposed to.
This is how the story has unfolded and what it means...
During the 2016 US presidential campaign, “The Wall” became Trump’s signature campaign promise, as he told supporters it was needed to stop drugs and criminals from entering the US.
Chants of “build the wall” became a regular feature at rallies both before he took office and after.
But opposition to spending billions of dollars on the project has been huge since day one and Democrats have consistently opposed it – as have the majority of the American public.
This political deadlock culminated in the New Year with the longest government shutdown in US history, as Democrats refused to give Trump the funding he was demanding to fund the wall.
Eventually, after 35 days where hundreds of thousands of federal workers went without pay, the president caved and announced he would sign legislation that will bring to a temporary end to the shutdown.
Crucially, he did not secure the $5.7bn (£4.4bn) he had demanded for his signature campaign promise, instead getting only $1.4bn (£1.08bn) to increase patrols and reinforce existing structures along the border.
Even long-time Trump supporters criticised him for backing down, with right-wing commentators such as Mike Cernovich and Ann Coulter branding him a “wimp” and a “broken man”.
Backed into a corner and with no other options, Trump declared a national emergency last Friday in a move that allows him to bypass Congress to use money from the Pentagon and other budgets.
The president painted illegal immigration and drug trafficking across the border as a national security threat.
It’s this decision which Trump is now being sued over.
Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, Virginia, and Michigan joined California in the lawsuit, Reuters reports.
The states said Trump’s order would cause them to lose millions of dollars in federal funding for national guard units dealing with counter-drug activities and redirection of funds from authorised military construction projects would damage their economies.
On Monday, a national holiday in the US, Becerra said: “Today, on Presidents Day, we take President Trump to court to block his misuse of presidential power.
“We’re suing President Trump to stop him from unilaterally robbing taxpayer funds lawfully set aside by Congress for the people of our states. For most of us, the office of the presidency is not a place for theatre.”
Three Texas landowners and an environmental group have also filed a lawsuit against Trump’s move, saying it violated the Constitution and would infringe on their property rights.
On Monday the hashtag #FakeTrumpEmergency was trending on Twitter.
The lawsuits won’t come as a surprise to Trump – when making his speech declaring a national emergency last week, he laid out what would happen in a bizarre section of his speech which he seemed to almost sing.
He said: “We will have a national emergency and we will then be sued, and they will sue us in the 9th Circuit, even though it shouldn’t be there, and we will possibly get a bad ruling and then we’ll get another bad ruling and then we’ll end up in the Supreme Court where we might get a fair shake.”
The lawsuits from the 16 states represent the first stage of this and they are seeking to show there is no national emergency at the border.
To do this, Becerra said “the best evidence is the president’s own words.”
When announcing the national emergency, Trump said: “I didn’t need to do this, but I’d rather do it much faster.”
This would appear to undercut the sense of seriousness of the situation that Trump has tried so hard to make the case for.
California governor Gavin Newsom in a statement: “President Trump is manufacturing a crisis and declaring a made-up ‘national emergency’ in order to seize power and undermine the Constitution.
“This ’emergency’ is a national disgrace.”
Newsom also tweeted a list of things he considered actual emergencies, such as “gun violence” and “climate change”.
Newsom’s comments tap into fears some in Trump’s Republican party have – if the president uses the law to declare this issue a national emergency then it could set a precedent that would allow a future Democratic president to unilaterally tackle gun crime or climate change, both issues Republicans have historically been reluctant to make major moves on.
The National Emergencies Act of 1976 has been invoked dozens of times by presidents without a single successful legal challenge. Congress has never defined a national emergency in the law.
Legal experts said Trump’s declaration could be challenged on at least two fronts: that there is no genuine emergency and that Trump’s action overstepped his powers because under the US Constitution Congress has authority over federal appropriations, not the president.
“The odds favour the president by a significant majority,” George Washington University Law School professor Jonathan Turley said. “He has the authority to make the declaration and he has the money.”
But the administration’s defence of Trump’s action may not be a smooth ride. Lawsuits could delay the use of funds the president is planning to tap, and legal experts said the bulk of funds may be tied up for years.
Trump is running for re-election next year and a loss would mean his presidency ends in January 2021. It is possible the legal fight over the emergency declaration might not be resolved by then.
“My guess is the money, the significant amount of money, won’t flow before the 2020 election,” Harvard Law School professor Mark Tushnet said.
So far Trump has not commented on the lawsuits, instead using Twitter to celebrate President’s Day and quote his favourite Fox News pundits.