The fourth rule is: Make the enemy live up to their own book of rules. You can kill them with this, for they can no more obey their own rules than the Christian church can live up to Christianity — Saul Alinsky
Sanders is using this as a tactic. Trump said during the campaign he would not touch Social Security and Medicare. Sanders is constantly and loudly reminding Trump of this and of other promises he made.
We can also make a point of pointing out when Trump cannot fulfill promises he made, like with dismantling Obamacare and bringing back factory jobs to the Rust belt and coal jobs to West Virginia. Republicans in Congress are now balking on killing Obamacare and the vast bulk of those jobs aren’t coming back.
Those jobs aren’t coming back because capitalism mandates things be done as cheaply as possible. Coal is in an irreversible decline because it’s being replaced by natural gas and renewable energy. No company will build a factory in the US to make widgets at a cost of, say, $100 each when they can be made in China and shipped here for $50. Trump threatens tariffs and trade wars. However, they don’t work. Unless he wants iPhones made here with a list price of $400 more than the current price.
So, make Trump live up to the promises he made that we like and point out when his promises never materialize, either because he never meant them in the first place or they simply can’t be done.