What's next in the legal battle over Trump's immigration plan

— -- A panel of three federal appeals court judges unanimously ruled Thursday to uphold a restraining order against Donald Trump’s controversial immigration action that temporarily bars refugees and citizens from seven predominantly Muslim countries. With this ruling, Trump's order remains on hold nationwide while legal battles rage across the country. Trump immediately took to Twitter, girding for a fight.

And in a press conference at the White House today, Trump said "we are going to do whatever is necessary to keep our country safe. We’ll be doing something very rapidly having to do with additional security for our country. You’ll be seeing that sometime next week. We will continue to go through the court process and I have no doubt we will win that particular case."

ABC News took a look at what happens next in this case, which can proceed on multiple parallel tracks:

The Case Can be Litigated in the Washington District Court

The parties to this case -- the states of Washington and Minnesota as plaintiffs and Donald Trump, Department of Homeland Security, Secretary of State Rex Tillerson, Homeland Security Secretary John Kelly, and the United States of America as defendants –- can litigate this case in a Washington state district court while a preliminary injunction temporarily halts Trump’s executive order. A White House source told ABC News on Friday that the Administration plans to defend the president’s travel ban in that lower federal court rather than fighting to immediately restore the ban by challenging yesterday’s 9th Circuit appellate ruling.

Justice Department Can Appeal the Preliminary Injunction to the 9th

Thursday’s ruling addressed an appeal by the Department of Justice seeking to overturn a Washington District Court’s temporary restraining order (TRO) that put the Trump’s executive order on hold for a short time. But in an unusual move, the appellate judges treated the district court’s TRO as a preliminary injunction, which is a longer-lasting restraining order that is subject to appeal. In light of the extraordinary circumstances of this case," the judges wrote, the TRO possesses the qualities of an appealable preliminary injunction.

The Justice Department can now appeal the preliminary injunction to the same 9th Circuit Appellate Court that ruled yesterday. The parties will argue whether or not the immigration ban should remain temporarily halted. The Appellate Court will consider the parties’ likelihood of success on the merits, which party is more likely to suffer irreparable harm," the balance of interests," and the public interests. Because this case will focus on the preliminary injunction, it can still be kicked back to the lower district court for trial on the merits to determine whether the immigration action is legal and constitutional.

The appellate court on Thursday set a briefing schedule for appeal, with court papers due March 3, March 24, and March 29.

This opinion is a narrow one, but forceful," said Anil Kalhan, a professor at Drexel University's Kline School of Law. The Republican administration faces an uphill road if it wants to appeal this order in the short term, but there is a lot litigation left to come before this is definitively resolved."

Justice Department Can File a Motion for Reconsideration

Within 14 days, the Justice Department can also file a motion for reconsideration of Thursday’s decision by the same three-judge panel or by an en banc" panel of 11 judges randomly selected from the Ninth Circuit Appeals Court. A majority of the appellate court judges, 13 out of 25, would have to agree to an en banc review, which is highly unlikely according Kalhan.

Justice Department Can Try to Take the Case the U.S. Supreme Court

On Friday, a White House source told ABC News that while the case may ultimately end up at the Supreme Court, for now, that is not the next step for the Trump administration.

Nevertheless, the Justice Department could seek a stay application" from the eight-member US Supreme Court. Without getting to the full merits of the case – that is, whether or not Trump’s executive order is legal and constitutional – five Supreme Court justices would be needed to stay (or halt) the Ninth Circuit and district court rulings and allow Trump’s immigration order to go back into effect while lawsuits nationwide proceed.

The Justice Department can also file a Petition for Writ of Certiorari which can be granted by four Supreme Court justices, although multiple experts told ABC News this would be extremely unlikely. In that scenario, the Supreme Court could technically begin deciding the underlying constitutional questions raised by Trump’s immigration order.

Legal Battles Across the Country Could Mean Conflicting Rulings

The lawsuit filed by the states of Washington and Minnesota is just one of the cases across the country currently challenging the president’s immigration ban. Notably, a federal appeals court in Brooklyn, NY has also issued a nationwide stay of the executive order for certain people that will last at least until February 21, when the parties next appear in court.

It is possible that over time different federal district courts and appeals courts will hand down conflicting rulings, which would be a basis for the US Supreme Court to take the case," notes Kalhan.

Trump Could Change the Executive Order and Render the Cases Moot

The Trump Administration is considering introducing another executive order in the wake of yesterday’s ruling, according to a White House official, who told ABC News that all options" are on the table.

Just two days after the executive order was signed, Department of Homeland Security head John Kelly backtracked on a key part of the immigration order, saying that green card holders would not be prevented from returning to the U.S. "absent the receipt of significant derogatory information indicating a serious threat to public safety and welfare." The appeals court on Thursday found these assurances inadequate: At this point, however, we cannot rely upon the Government’s contention that the Executive Order no longer applies to lawful permanent residents," the judges wrote. Nor has the Government established that the White House counsel’s interpretation of the Executive Order is binding on all executive branch officials responsible for enforcing the Executive Order."

Donald Trump, as Washington Attorney General Bob Ferguson suggested Thursday night, "can tear up his executive order and start over." If that happens, these lawsuits could become moot and new legal battles could start from square one.

ABC News' James Hill, Jonathan Karl, Kate Shaw and Cecilia Vega contributed to this report.