Trump is simply not subject to laws

The White House late Tuesday signed a memo allowing troops stationed at the border to engage in some law enforcement roles and use lethal force, if necessary — a move that legal experts have cautioned may run afoul of the Posse Comitatus Act.

The new “Cabinet order” was signed by White House Chief of Staff John Kelly, not President Donald Trump.

  Military Times

How is that allowable? I can see why Trump would want to avoid putting his signature on it, but how is his Chief of Staff in any way permitted to give military orders?

Some of those activities, including crowd control and detention, may run into potential conflict with the 1878 Posse Comitatus Act. If crossed, the erosion of the act’s limitations could represent a fundamental shift in the way the U.S. military is used, legal experts said.

The Congressional Research Service, the non-partisan research agency for Congress, has found that “case law indicates that ‘execution of the law’ in violation of the Posse Comitatus Act occurs (a) when the Armed Forces perform tasks assigned to an organ of civil government, or (b) when the Armed Forces perform tasks assigned to them solely for purposes of civilian government.” However, the law also allows the president “to use military force to suppress insurrection or to enforce federal authority,” CRS has found.

[...]

Defense officials said the language in the directive was carefully crafted to avoid running up against the bedrock legal limitations set in Posse Comitatus. The law was originally intended to protect the states from being controlled by federal troops. It has evolved into a singly defining, almost church versus state-type wall forbidding active-duty forces under the control of the president from conducting any types of crowd control or law enforcement domestically, essentially ensuring that the U.S. military is not used to control or defeat American citizens on U.S. soil.

Kelly said in the signed directive that the additional authorities were necessary because “credible evidence and intelligence” have indicated that the thousands of migrants who have now made their way to the U.S. checkpoint near Tijuana, Mexico, “may prompt incidents of violence and disorder” that could threaten border officials.

But the White House still may find itself in a legal challenge if the authorities in the memo are determined to be counter to the law, Banks said.

“Even [an executive order] couldn’t overcome Posse Comitatus,” Banks said.

President Donald Trump this week presided over an explosive meeting on a new Cabinet order granting the troops deployed at the southern border the right to use lethal force to defend border patrol agents.

Several White House aides and external advisers who have supported the president’s hawkish immigration agenda attended the Monday meeting, which devolved into a melee pitting two of Trump’s embattled aides, White House chief of staff John Kelly and Department of Homeland Security Kirstjen Nielsen, against other attendees, according to three people briefed on the exchange.

  Politico

Word has it that those two are on their way out the door, and not voluntarily.

Kelly and Nielsen initially argued against signing the declaration [...] telling the president that the move was beyond his constitutional powers. They were vocally opposed by, among others, senior policy adviser Stephen Miller; Chris Crane, president of the National Immigration and Customs Enforcement Council; and Brandon Judd, president of the border patrol union. Also present was Vice President Mike Pence, who did not take a stand on the issue, according to one of the people briefed on the debate.

He'll be finding himself out the door in 2020, too, I'm willing to wager.

[T]he bitter dispute ended Tuesday evening when Kelly, on Trump’s orders, signed a Cabinet declaration granting the military the disputed authority. The move ran afoul of the guidance offered by the White House counsel, Emmet Flood, who cautioned that it was likely to run into constitutional roadblocks, according to a second source familiar with the conversations.

Emmet's not guaranteed a job, either.

Nielsen disputed the account in a statement sent after publication, calling [it] "a complete fabrication."

"While a range of issues were discussed on a Monday call, the cabinet memo was not one of those topics. In reality, I have been clear: our agents and officers must have the ability to protect themselves, and to be protected by others, if they face critical situations on the border," the statement said. "I have been and will continue coordinating closely with Secretary Mattis to ensure that our people have the support and protection they need to do their jobs."

She'd really like to keep her job till the end of the year, at least.

The president’s move on Tuesday is also illustrative of the extent to which, on immigration in particular, he has stretched the limits of his constitutional powers, preferring to issue executive orders rather than work through Congress. It’s an instinct that has been encouraged by advisers like Miller, who have pointed out that previous presidents have extended the powers of the executive branch further.

[...]

The final order appeared to take Defense Secretary James Mattis by surprise, an indication of the extent to which immigration policy in the Trump White House is engineered by a small group of hawks, including Miller — and, as a result, has often caught other stakeholders off guard.

[...]

He also suggested he was aware that Kelly had signed the order at Trump’s insistence: Kelly “has the authority to do what the president tells him to do,” Mattis said, adding that regardless of what he himself is asked to do, he will not order troops to violate the law.

Things are getting extremely tense in the Trump administration.  And, no, Mattis' job isn't guaranteed, either.

...but hey, do what you want...you will anyway.