Spoilers ahead for the Season 4 premiere of Supergirl, called "American Alien."
Supergirl returned for its fourth season on a brand new night, and the time slot isn't the only difference for the Girl of Steel. The premiere revealed a Supergirl who has mastered balancing her superheroics with her life as Kara Danvers, even picking up the slack for Superman while he's off-planet. Unfortunately, despite her belief that everything is getting better, she encounters a new threat that proves Earth is more dangerous than ever for aliens, and superpowers won't be enough to defeat the bad guys this time around.
We've known for a while that the big bad of Season 4 won't be other alien with superpowers, as new big bad Agent Liberty would be a threat more due to his influence than his physical capabilities. Liberty himself only appeared at the very end of the episode for a few moments (and behind a mask), but the rest of the episode revealed a network in place for Liberty and his followers to do a lot of damage to aliens attempting to live peacefully on Earth.
Although Agent Liberty will be the head of the Earth First movement and primary antagonist (complete with his own origin story episode), Mercy Graves and her brother Otis represented the bad guys in "American Alien." They staged a break-in at a tech company and made off with an EMP, although not without assaulting an alien employee and cutting off his tusks to gain access to a secure room.
After failing to stop the Graves siblings once they used technology specifically designed to counter her superpowers, Kara decided that the assault on the alien employee was all because of the burglary and not because of any particular ill-intent against aliens. J'onn J'onzz disagreed, arguing that brewing anti-alien sentiment resulted in the attack, making it a hate crime. Otis Graves certainly did take a sick joy in his assault, and the second tusk didn't even need to be cut off for the EMP theft.
Kara and J'onn were on opposite sides of the argument for most of the premiere, as Kara believed President Marsdin's upcoming celebration of the Alien Amnesty Act was a hallmark of an era that has gotten better for aliens, while J'onn believed that the Alien Amnesty Act was only stirring up resentment among some humans who didn't like the aliens living among them. Kara wasn't willing to hear J'onn's side of the story until she had no choice but to face the growing anti-alien sentiment.
With the surprising help of Lillian Luthor, Kara and the D.E.O. were able to track the Graves' headquarters to an abandoned warehouse, because whether the action is taking place on Earth-1 or Earth-38, there are always abandoned warehouses for shady individuals in the Arrow-verse. This particular warehouse had been used by Cadmus. Mercy and Otis weren't there, but Kara discovered onething more frightening than a couple of new bad guys. She found a hub of online communication between people who don't want aliens around.
There were chatrooms of people looking for ways to take out aliens, including one person looking to make a bomb to take out an alien at her son's school. Posts referred to aliens as "roaches" and claimed that aliens stole human jobs and were "hiding" in human communities. One post even bragged about smashing alien cars.
Unfortunately, the chat rooms filter through the dark web, so they were untraceable even for Brainy as Winn 2.0. He did discover onething that Mercy and Otis failed to purge from their systems: the blueprints for Camp David, a.k.a. the location of President Marsdin's summit in honor of the second anniversary of the Alien Amnesty Act. Kara came to the conclusion that they were targeting the event, and she tried to warn Marsdin to cancel.
Marsdin -- who fans will remember is actually an alien herself, posing as a human and getting herself elected to the highest office in the land -- refused to cancel. The good news is that neither Mercy nor Otis were able to assassinate Marsdin. The bad news is that by using the stolen EMP and disguising themselves as D.E.O. agents, they set a chain of events in motion that resulted in Marsdin being caught on camera in her natural form, definitely not looking an awful lot like Wonder Woman.
Kara caught Otis Graves, but Mercy escaped after delivering this frightening message:
The episode didn't reveal what's going to happen to President Marsdin, but the casting of her vice president as a recurring character points toward Marsdin losing her office. All things considered, Marsdin being outed as an alien could be the very worst thing that could happen to the alien population living peacefully among the people of the United States. For people already paranoid and angry about aliens, the reveal that the president deceived her way into the highest office in the land undoubtedly won't calm them down.
When Agent Liberty steps out and really begins to rally folks into his hate group (with the continued help of Mercy Graves), he could find a fertile field of people willing to sign on with his humans-first agenda. People who were already showing their true colors in chat rooms might feel motivated to do onething about their frustrations, and there's no way that could end well for the innocent aliens who thought they were safe under the Alien Amnesty Act.
In fact, we now have to wonder what will happen to the Alien Amnesty Act. It has been shaping policy for two years by this point in the Supergirl timeline, but perhaps the reveal that Marsdin is an alien will give people in the government who hate aliens reason to try and get it undone. As J'onn made the sad point to Kara early in the episode, aliens who can pass as human without altering their appearances have an easier time than others.
A lot of aliens could be in a lot of trouble, and Kara can't just punch this threat into submission and lock it up in the D.E.O. All of her superpowers can't fix this problem, and it's frighteningly possible that she'll lose her standing as a celebrated hero of the people. The episode ended with the reveal that Kara's doppelganger (from the Season 3 cliffhanger that revealed the Red Son arc in the works) is being directed to use her superpowers in Kasnia in a way that nearly resulted in a massive train crash.
If a seemingly evil Supergirl emerges and begins using the same powers Supergirl has to wreak havoc, paranoid humans could begin to consider Supergirl an enemy as well. Kara is going to need all the help she can get in Season 4. Perhaps she'd welcome a visit from her cousin sooner rather than later! We can't say at this point if she'll hang out with her Earth-1 pals ahead of the gigantic crossover, so we'll have to wait and see.