Why Trump Temporarily Stopped Immigration

He may have done that to toss some raw meat to his base, but his main reason has to do with narcissism (see this post for more information):

Narcissists play games.  All debates are games, and a narcissist must win all such games.  When it becomes clear that a narcissist might not actually win a particular debate, he or she will first try to turn the tables in that debate*, but if this cannot be done, the next solution is to start new games, games which the narcissists know they will win.  And those new games must be made so attractive to others that they forget to play the game the narcissist was losing.

Trump cannot win the conversation about how competent he has been in leading the country during this pandemic, and so he doesn't want that game played anymore.

To lure the media, and the rest of us, away from the game he wishes to be buried, he offers us alternative games, truly outrageous ones, and because he is very good at being a narcissist, the games he creates are like shiny baubles for magpies:  Journalists will flock to report on them, and this makes it less likely that Trump will have to lose the debate about his incompetence.

Those recent alternative games he has set up include his claim that masks in hospitals are rare because health care workers are stealing them, his de-funding of the World Health Organization,  and now his decision to temporarily stop all immigration to the US**.

Whatever other reasons he may have had for starting those particular games, their major function is to shift the play away from the one game he does not wish anyone to play.  And that is the question how well or poorly he is leading the country during a pandemic.

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*  My description of the narcissistic games here is kept simpler than how such games actually work.  When I write "turning the tables" I mean the trick of taking whatever someone is being accused of and simply reversing that argument or finding comparable arguments that can be used against the original accuser.  In a sense those, too, are alternative games.

And of course many people who are not narcissists play some of those games, too.  The difference is that the narcissist always plays these games, always, and never admits to any kind of defeat.

** This particular alternative game is so very clearly intended for only that purpose.  Immigration is not exactly booming during this pandemic, and Trump cannot currently defend his immigration move as an attempt to protect Americans against the virus coming from abroad, given that the virus is already here and raging.