MYSTERY TRAIN: If North Korean leader Kim Jong Un was on that heavily armored mystery train that pulled into Beijing under a cloud of secrecy and then left the next day, it would mark his first trip outside of North Korea since taking power in 2011.

Neither China nor North Korea is confirming who arrived on the train and was subsequently escorted through Beijing under heavy security. It could have been Kim, or a high-level envoy such as his sister, as preparations continue for next month’s planned meeting between Kim and South Korean President Moon Jae-in and President Trump in May.

Bloomberg quoted “three people with knowledge of the visit” as confirming that Kim was indeed the mystery guest. But The Associated Press quoted South Korean analysts who said it was unlikely he would sneak into Beijing for his first face-to-face meetings with the Chinese leadership, suggesting it was more likely that Kim sent a special envoy, possibly his younger sister, Kim Yo Jong, to appease China ahead of his planned meetings with the U.S. and South Korean presidents. AP also has a story on what makes this train different.

IRAN DEAL DEPARTURE: Trump is “prepared to potentially withdraw” from the Iran nuclear deal if changes to the agreement aren’t made, White House principal deputy press secretary Raj Shah told reporters yesterday. “The president’s been pretty clear… what he thinks of the Iran deal,” Shah said. “He thinks it’s one of the worst agreements the United States has ever made internationally. And he is insistent on changes, both at the congressional level in working with Congress and also with our European partners.”

Shah’s statement came in response to a question about reports in the Israeli media that Prime Minister Benjamin Netanyahu has begun informing French and German foreign ministers that the U.S. is very likely to pull out of the Iran deal in May.

Meanwhile, 115 national security leaders have signed a new statement titled “Keep the Iran Deal — 10 Good Reasons Why.” It includes 49 retired senior U.S. military; 19 former members of Congress and 29 former U.S. ambassadors (five of them are former U.S. ambassadors to Israel). Among the signatories is Michael Hayden, former director of national intelligence.

“I was never a fan of the arrangement, I thought that we could have demanded a better deal, especially since Iran should have been the supplicant here, not us,” Hayden writes in a post on The Cipher Brief. “Still, Iran is further away from a weapon with this agreement than they would be without it. And American intelligence is more knowledgeable about Iranian nuclear developments because of the deal and its inspection regime.

“Using the nuclear deal and re-imposing sanctions is like beating Iran with our carrots and ignoring our sticks. It could also prompt the Iranians to resume their nuclear program and it would no doubt isolate us from our European friends.” Hayden argued.

THE GREAT RUSSIA EXPULSIONS: The United States has joined Canada, Australia and most of Europe in expelling more than 100 Russian diplomats in a coordinated response to the nerve agent attack on former Russian intelligence officer Sergei Skripal and his daughter in Britain. British Prime Minister Theresa May has been privately sharing intelligence that is said to point directly to the Kremlin and Russian President Vladimir Putin.

Apparently convinced, Trump ordered the expulsion of 60 Russians who the U.S. says are actually intelligence officers, in other words, spies. A dozen of the diplomats were assigned to the United Nations in New York, while the other 48 work at Russian embassies and consulates around the country. The administration is also ordering Moscow to close its consulate in Seattle.

WHY SEATTLE? White House press secretary Sarah Sanders released a statement that said the Seattle consulate closure is due to its proximity to a U.S. submarine base and Boeing. Naval Base Kitsap, which is about a 90-minute drive from Seattle, houses the Navy’s West Coast-based Trident ballistic missile submarines.

RUSSIA’S REACTION: Anatoly Antonov, the Russian ambassador to the U.S., hit back after yesterday’s announcement. The U.S. “took a very bad step by cutting what very little still remains in terms of Russian-American relations,” Antonov said. “We are to analyze the situation following the declared decisions by a number of countries to expel our diplomats,” said Dmitry Peskov, spokesman for Putin. “The main analysis will be done by our Foreign Ministry. After that the president will see proposals for taking retaliatory steps. A final decision will be made by the head of state.”

AND A BIT OF TROLLING BY THE EMBASSY: The Russian embassy in Washington, D.C., polled Twitter users on Monday asking which American consulate it should close in response to Trump’s decision. The embassy provided three choices: the U.S. consulates in Vladivostok, Yekaterinburg, and St. Petersburg. As of this morning, more than 53,000 Twitter users had voted with three hours to go before the poll ends.

SUSPICIOUS PACKAGES: The Pentagon is confirming that a number of suspicious packages sent to multiple military installations in the Washington, D.C., area yesterday are being investigated by the FBI. According to media reports last night, the packages were mailed to Fort McNair and Joint Base Anacostia-Bolling in D.C., Fort Belvoir and a naval support facility in Virginia, and a CIA mail processing facility in Virginia. NBC also reported that a package was found at a White House mail-processing space.

A package that tested positive for “black powder and residue” prompted an evacuation of the National Defense University at Fort McNair, according to Army spokesman Michael Howard, who in a statement to CNN said, “The X-ray conducted indicates suspected GPS and an expedient fuse were attached.”

Good Tuesday morning and welcome to Jamie McIntyre’s Daily on Defense, compiled by Washington Examiner National Security Senior Writer Jamie McIntyre (@jamiejmcintyre), National Security Writer Travis J. Tritten (@travis_tritten) and Senior Editor David Brown (@dave_brown24). Email us here for tips, suggestions, calendar items and anything else. If a friend sent this to you and you’d like to sign up, click here. If signing up doesn’t work, shoot us an email and we’ll add you to our list. And be sure to follow us on Twitter @dailyondefense.

TRANSGENDER COURT HEARING: A federal court in Seattle will hold the first hearing today on transgender military service since Defense Secretary Jim Mattis unveiled a new set of personnel policy recommendations on Friday. Rights groups hope to win a summary judgment that would permanently stop the Pentagon from rolling back the Obama administration’s open service policy. For now, the Pentagon is temporarily blocked from changing the policy by four injunctions in four separate federal lawsuits.

But Trump’s Justice Department has filed motions in those cases to dissolve the injunctions. If granted by all four courts, the move could allow the Pentagon to move forward with a new transgender policy. The department is arguing that litigation should focus on the newly released Mattis policy proposal and not Trump’s tweeted announcement last year of a complete ban on transgender troops. Opponents have been battling in court to determine if Trump consulted with military leaders before tweeting about an all-out ban in July.

MATTIS MUM ON NEW POLICY: Mattis’ new policy proposal stops short of Trump’s all-out ban, but could bar many transgender people from serving in the military. And the defense secretary is not talking about it. “We are out to build the most lethal service,” Mattis said in response to reporter questions at a press availability with the Indonesian foreign affairs minister yesterday. “Because these are matters under litigation I am not going to discuss them further.” When reporters pressed him on why some transgender troops can serve and other can’t, Mattis said only, “I think the statements stand on their own right now.”

DON’T CHANGE, DON’T COMPLAIN: The first thing to understand about the new policy is that technically it’s not policy yet. As Mattis correctly points out, the courts have still not ruled on whether it is constitutional to bar service by transgender troops based on their gender identity, and not solely only their ability to perform their jobs.

Trump’s order did not set policy, but instead granted Mattis’ request to leave the details to him, and in the case of the Coast Guard, Homeland Security Secretary Kirstjen Nielsen.

The policy outline by Mattis in his February memo to Trump has two big exceptions, and creates two classes of transgender troops. Those troops already serving under current policy “may continue to serve in their preferred gender and receive medically necessary treatment for gender dysphoria.”

Those who consider themselves transgender may join after the new policy takes effect, but may serve only in their “in their biological sex,” and as long as they have had no reconstructive surgery, no “history or diagnosis of gender dysphoria,” and don’t require any “substantial medical treatment, including through medical drugs or surgery.” Sound a lot like the “Don’t Ask, Don’t Tell,” compromise that allowed gays to serve in the military in the 1990s, although not openly.

You can read our FAQ on what we know and don’t know about the proposed policy here.

F-35s FOR TAIWAN: Sens. Jim Inhofe, a senior Senate Armed Services member, and John Cornyn, the majority whip, are urging Trump to commit to selling ally Taiwan advanced F-35 fighter jets to counter a growing military threat from China. “The survivability of the F-35B and modern long-range sensors could help Taiwan intercept Chinese missiles, promoting deterrence well into the next decade,” Inhofe and Cornyn wrote in a Monday letter to Trump. “The F-35B would not only provide a modern fifth-generation fighter, but would also bolster their capabilities in next-generation warfare.”

Taiwan President Tsai Ing-wen has inquired about purchasing the vertical takeoff and landing “B” variant used by the Marine Corps. The sale of the fifth-generation jets, made by Lockheed Martin, could help the island nation replace its F-16 Fighting Falcons bought from the U.S. in 1993. Taiwan can field only 65 of the F-16s at any given time due to foreign deployments and an ongoing upgrade program, the senators said. The number “is not enough to maintain a credible defense,” Inhofe and Cornyn wrote.

TIGHTENING ACCESS: The Pentagon is instituting a new visitor policy effective next month that will require anyone who does not have a Pentagon access pass to be pre-registered in a computer database one business day in advance of any visit (two days ahead for any non-U.S. citizen). The new Visitor Management System will be used for all official visitors, employee family members, personal guests, and news media members without official credentials.

The new rules take effect April 2. More details here.

THE RUNDOWN

AP: Mattis appears isolated as Trump adds hawkish Bolton

AFP: In ‘city of shanasheel’, Iraqi heritage crumbles from neglect

BuzzFeed: Welcome to the Donald Rumsfeld-Liz Cheney restoration.

Air Force Times: DARPA wants to ‘slow life to save life’ with program that extends the ‘golden hour’

Business Insider: A crazy viral video showing Saudi Arabia destroying Iran’s military is now more relevant than ever

Army Times: As the Army turns to functional fitness testing, is the end of gender standards near?

Foreign Policy: Saudi Arabia Faces Strong Headwind in Congress Over Yemen

Washington Post: North Korean Economy Apparently Stable

Breaking Defense: Can’t Stop The Signal: Army Strips Down Network To Survive Major War

Defense News: The Army of 2028 will be ready to fight any war, top civilian says

Navy Times: Navy conducts F-35C qualifications aboard aircraft carrier

USNI News: Concept for Lockheed MQ-25A Stingray Unmanned Tanker Bid Revealed