Today Muhammad Ali Jr. was detained by border agents as he returned to the US from Jamaica. He was held for nearly 2 hours as they repeatedly questioned him about his religion, where he was born, and his name. He's considering legal action.
This sort of thing did not happen before Trump's election. Trump wants to ban Muslims and border agents are acting on his wishes even though courts have thrown out his first executive order aimed at enacting that ban.
This is blatantly unconstitutional and there are only a couple of ways this can go.
The most unlikely direction is that this sort of discrimination becomes the new normal and we become a less open and diverse country, realizing the ideal of white nationalists like Steven Bannon. The implications of this direction are so dire - our universities, corporations, conferences, tech hubs, intellects and inventors all become second rate as the best in the world begin to choose new places to learn, work, live, and collaborate. Too many rich and powerful people will oppose this to allow people as small as Trump and Bannon to vandalize our country like this. This is certainly a possible outcome but it is unlikely to be sustainable.
A more probable outcome is that this gross infraction of constitutional law will prove to be temporary. At that point the border agents engaged in this behavior will have to be prepared for investigations that could result in legal action against them. Unconstitutional behavior has consequences for everyone from president to entry-level agent. The only reason there is currently no consequence for this is because Republicans have the House and Senate and they don't care about constitutional niceties nearly as much as they care about offending Trump and his base and exploiting a monopoly on power to get their agenda passed. But when they lose even one branch of Congress, the investigations will begin. Once a special investigator was appointed for Watergate or Lewinsky, impeachment followed and nobody in Congress could stop that train. This will happen eventually. Either the Republicans do it now or the Democrats will do it later. And when it does, border agents and people throughout the organization below Trump will either be on the side of the constitution or find themselves in legal trouble.
It might be exciting to go against the constitution in pursuit of some grand vision but American history isn't kind to parties who do. Rather than being excited about the opportunity to crack down on people they don't care for, border agents might think about trouble with other people they don't care for: lawyers. It's wildly improbable that any of the Muslim immigrants or visitors that worry them will take action against them; it is distinctly possible that lawyers will. This might be worth considering.