So another Cabinet member in President Donald Trump’s administration has departed abruptly, this time the hapless and much vilified Department of Homeland Security Secretary Kirstjen Nielsen. Nielsen, you’ll remember, came to occupy the post courtesy of a recommendation from former Chief of Staff John Kelly, a once-respected general who was regularly humiliated by Trump until he too left.

Within 24 hours of Nielsen’s departure, Trump fired Secret Service Director Randolph Alles, who reported to Nielsen.

The problem is not just that Trump’s high-level appointments have the shelf life of a high school crush. The disturbingly common thread is that no matter how high-level the appointment, the official’s standing depends on his or her willingness to advance Trump’s agenda at all costs. Whether the idea at hand is lawful, defensible or practical does not enter the equation.

Nielsen presided over horrific policies that separated families seeking asylum, that kept children detained in cages. But that wasn’t enough. Trump also has expressed a desire for “tougher” policies, and has said he would like to dispense with asylum and immigration judges and has threatened to close the border entirely. According to news reports, Nielsen’s disagreement and search for alternatives in a meeting with the president ended instead with her resignation.

Those who stay must be willing to defend the indefensible and then endure reversals by Trump and even get blamed for the idea they privately opposed. (Witness the recent verbal gymnastics of Education Secretary Betsy DeVos on Special Olympics funding.)

The roll call of the departed is too long to list here, but it takes in former Secretary of State Rex Tillerson, former Attorney General Jeff Sessions and a host of others who together make for the highest turnover rate in modern presidential history.

That has left Trump to appoint a number of “acting” officials — a practice he has said he prefers to Senate confirmation. The advantage? He sidesteps even the nominal challenge that might be posed in such hearings, and, he believes, acting officials give him more “flexibility.”

These are further incursions into this country’s governing norms that should be resisted. Trump clearly views laws that run contrary to his wishes as temporary impediments, to be challenged and, if possible, eliminated. Underlings who do not share that view quickly find themselves unwelcome.

Nowhere is this more evident than in the self-created crisis at the border. Before Trump took office, illegal immigration into this country was at near-historic lows. The uncertainty fostered by his constant threats is creating a stampede mentality, where desperate families are rushing the border in their quest for asylum because they don’t know what might come next.

Trump’s national emergency declaration, which was designed to grab funding for his wall, still stands because Republicans in Congress were unwilling to oppose him. He wants to halt foreign aid to the so-called Northern Triangle countries of El Salvador, Guatemala and Honduras, though that will likely only exacerbate the exodus from those countries.

More chilling is the president’s assertion that the U.S. is “full” and can accommodate no more. That premise, if accepted more broadly, would be a license to crack down on all forms of immigration to this country, legal and otherwise.

The Senate should find a way to push back. Trump will soon have a Cabinet of temporary underlings who have little agency of their own, but are dependent on the whim of one man.

That is not what the founders of this country intended.