On May 15th, a three-judge panel of the president's least-favourite federal court heard Mr Trump's plea to reinstate his revised ban on travel from six Muslim-majority countries.
Trump's attempted travel bans have caused the number of refugees coming into the U.S.to plummet in the last two months, despite his executive orders largely being blocked in the courts.
Neal Katyal, former acting solicitor general under President Obama, represented the challengers - the state of Hawaii and a local imam.
Whether the president meant to target members of a particular religion matters because a key argument by Hawaii - and other plaintiffs suing over the travel ban across the country - is that the executive order amounts to a violation of the establishment clause of the Constitution, which prohibits favoring or disfavoring members of a specific faith.
The revised travel ban that Trump signed on March 6 would block the entry of foreign nationals from six majority-Muslim countries for 90 days, with exceptions for permanent US residents and current visa holders, and suspend the admission of refugees for 120 days.
Judge Richard Paez called the president's pre-inaugurations comments "profound" though necessary to view through the perspective of heated campaign rhetoric. The Justice Department counters that Trump was exercising his legal authority by issuing the order and say the lower courts have wrongly second-guessed him on matters of national security.
A Trump administration lawyer says the president's travel ban is nothing like the internment of Japanese citizens during World War II.
If Trump's executive order was the same as the one involving Japanese Americans, Wall said: "I wouldn't be standing here, and the US would not be defending it".
Both times, though, it seemed clear that the end result might well be a decision that, even if narrow, could actually work to bar the presidential executive order that targets travelers from Mideast nations.
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The Justice Department separately appealed a different federal judge's decision to halt the 90-day travel ban to the 4th US Circuit Court of Appeals. The government argues that multiple court rulings striking down his original January 27 travel ban and blocking implementation of his revised order have set unprecedented limits on the president's authority to regulate the country's immigration policies. In December 2015, Mr Trump called for a "total and complete shutdown" on Muslims entering the country; shortly thereafter, he said "Islam hates us".
"This order is aimed at aliens overseas, who themselves don't have constitutional rights", Wall said during the hearing broadcast live on C-Span and other news stations.
Three ninth circuit judges questioned an attorney for the President about statements made during the campaign regarding Muslims.
Katyal said no, and suggested the president could begin by repudiating his earlier statements or by working with Congress.
White House spokesman Sean Spicer told reporters on Monday that the administration was confident the executive order would be upheld by the appeals court. The injunction against the travel ban remains in place until the Ninth Circuit rules.
Dozens of activists gathered Monday morning, some carrying "No Ban, No Wall" signs. How those laws might authorize or constrain Trump's actions is a key aspect of the travel ban cases. The judges will decide whether to uphold a Hawaii judge's decision in March that blocked the ban.
ROSE: A lawyer for the administration said President Trump was a private citizen - he was candidate Trump - when he said those things, he was not making official policy when he made those statements, and that the president has since clarified his position since he took office.
U.S. District Judge Derrick Watson in Hawaii blocked 90-day entry restrictions on people from Libya, Iran, Somalia, Sudan, Syria and Yemen, as well as part of the order that suspended entry of refugee applicants for 120 days.
This isn't the first time the 9th Circuit has been tasked with deciding the immediate fate of the president's travel ban. They peppered Acting Solicitor General Jeffrey Wall with questions about whether they could consider Trump's campaign statements calling for a ban on Muslims entering the U.S.