16 states led by New York and California are taking legal action to stop President Trump's partial ban on immigration.
The move came as protests grow, with some demonstrators gathering at the White House to express their fury over the weekend's developments.
And there's still widespread confusion about the precise restrictions the US President has authorized, as our Washington Correspondent Simon Marks reports.
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At airports in Philadelphia……
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In Los Angeles…..
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And on the doorstep of the White House itself,
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Protestors took to the streets all over America on Sunday to express their outrage at President Trump's executive order.
It was signed with a flourish late on Friday afternoon….at the time he called it "good stuff" as he closed America's borders to people from 7 mostly-Muslim countries, and temporarily terminated America's willingness to accept refugees.
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That was Donald Trump on Saturday….insisting the ban was working just has he had intended.
But in fact, his order had created chaos….at airports, where immigration agents were scrambling to get clarity on what the new rules required.
And behind the scenes at the White House, where the President's top officials were inundated with questions they couldn't answer.
White House Chief of Staff Reince Priebus took to NBC's "Meet the Press", saying the White House would….
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But then, his interview went off the rails.
He appeared to indicate that green card holders - permanent US residents from the countries affected by the ban - would no longer be subject to it.
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Within moments, though, he had contradicted himself and it is still completely unclear whether permanent residents can come and go at will, as their green card status previously allowed…or whether they, too, will be caught in the President's net.
Democrats assailed the President….their leader in the US Senate Chuck Schumer tearing up at a press conference on Capitol Hill.
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And the Attorneys General from 16 states, all Democrats, came together to call President Trump's action "unlawful, un-American and unconstitutional"….they vowed to fight it in the courts.
It is, though, Republican criticism that will probably cause more concern in the White House.
Senators John McCain and Lindsey Graham called the action "hasty", and a "self-inflicted wound".
Senator Rob Portman is a Republican from Ohio.
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There could be further unforeseen fallout for President Trump.
Iran and Iraq are reportedly thinking of retaliating, by implementing their own new restrictions on US travelers.
Late on Sunday, the President put out a statement insisting that the restrictions do not constitute a Muslim ban….he blamed the media for misreporting them.
He seems to relish the legal battles that lie ahead but it's very early in his Presidency for a flashpoint that will test the constitutionality of his executive action.
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