Could they make the argument that they're checking for malicious software/viruses/other bad stuff that could be a threat to Americans?

What year is this? That kind of stuff can just be transferred via the Internet. It doesn't have to physically be transferred across the border.

Then we better put up a great firewall.

Also... Malware is not illegal. Using it can be.

Then "randomly" and arbitrarily searching people's devices as they cross the border isn't really an efficient way to do it, unless you also set up an intrusive firewall to "protect" the U.S. from malware.

I mean, not really unless they open it up and run antivirus software on it.

And even then it would only find things they already know exist, which would mean they're already in the country more than likely.

Contraband can be both physical and digital. If the government can conduct searches for physical contraband then searches for digital contraband in certain circumstances like border crossings seems reasonable.

Contraband can be digitally transmitted without physically traversing a border. Given this, what purpose is there to performing extended searches (potentially of cloud / remote data) at the time of border crossing?

This opens a door to unlimited search power at US borders against US citizens. There is already a 100-mile inland range where your can be searched without a warrant around our borders -- we are only going to make this worse by extending that range into all of our private digital data.

I posted a house/key analogy just now that may help clear up the distinction between physical and digital data search. Just to be clear, I'm actually ok with border guards physically inspecting my electronics. I am not ok with them compelling me to login to them, decrypt them, or otherwise hand them over my social media / banking logins / etc.

Keep in mind, we're talking about US citizens re-entering their own country here. I think this is a key point.

It could make sense for foreign visitors (to check for intended visa violations, etc.)

But there is no reason to search the devices of U.S. citizens and lawful permanent residents, who are already authorized to live and work in the U.S. These people would have no reason to break immigration law. And if the government is searching digital content for evidence of other unlawful activity, they should have to get a warrant.

Keep in mind that any digital content you can bring through a border port-of-entry, you can also just send it via the Internet.

The idea of digital contraband is anathema to a free society.