If so, there's nothing preventing him from doing that.

Deportations have to be negotiated with the receiving nation, regardless of whether we have a declared emergency or not. You can't just send somebody back without approval (otherwise you're facilitating an invasion), so each individual case has to be processed by both the US's immigration departments as well as whichever country you're trying to deport that person to. It doesn't happen often, but there are situations where a receiving country could outright refuse a deportee, or may be otherwise unable to receive them (perhaps the person isn't a recognized citizen of that country, either).

Deportation isn't as swift of a process as a lot of people think. Many deportees spend weeks or months in detainment before they're ever released. The system would be immediately backlogged if they were to move at rates Trump is suggesting.

There's also the issue of sending civilians into active warzones. Many immigrants are refugees, escaping from countries that are at war. Take Haiti for instance: They're in the process of being taken over by gangs, and their government is in shambles trying to combat them. Their president was assassinated a few years ago, and kidnappings of civilians are on the rise. Civilians are not safe in Haiti right now, and sending people into an active conflict like that could be seen as a crime against humanity.

There will be deportations. Hundreds, maybe thousands. But definitely not millions.

And, it's also more likely that the Biden administration will cooperate giving them the information they'd need to take legal action under Trump.

You beat me to it.

In isolation, no one can do anything. But if people organize in large numbers and share the risk, they can be a real force of resistance.

It's just stupid news. It adds nothing to the conversation and they talk it up as if it will change something. I get what they do, but nothing short of widespread resistance will change it. A week long nationwide work stoppage would do it