Even before Trump border control officers already had way too much power.

I worked for a company that considered the US border only second to the Chinese border in terms of a risk to confidential information. If you went to China, you had to sign out a special laptop that was wiped clean of anything confidential. Going to the US, you were allowed to take your own work laptop, but they had special briefings detailing what to do in various situations to try to keep the company’s data confidential while complying with the warrantless searches at the border.

What it comes down to is who cares. In this case, the general public doesn’t care. The TSA / Homeland Security wants to be seen to be doing everything possible. At first it was about terrorism, then it became about child sex abuse imagery that apparently people were going to take across the border, unencrypted on their work laptops. So, the boundaries of what was reasonable to search for just kept getting expanded. A few civil rights orgs. and people who cared about privacy tried to push back, but even though they cared a lot about this issue, the general public didn’t care, so Homeland Security got even more rights to search.

IMO it’s the same reason why the US is essentially the only country that does citizenship-based taxation rather than residency-based taxation. The vast majority of citizens don’t care because they never work outside the US. The government cares because it’s free money, and sometimes they get to take money from mildly rich people who try to evade US taxes by moving to a tax haven. But, the vast majority of people who have to deal with these taxes are low and middle-income people who have dual citizenship and live in Canada, or are Americans who took a job overseas. They all hate having to file these taxes, and think they’re completely unfair, but it’s just too small a group for the government to care about.