Warning: spoilers ahead for Episode 3 of Supergirl Season 3, called "Far From The Tree." You may want to check out some of our other articles until you get the chance to watch.
Supergirl sent Kara and J'onn to Mars to reunite with Miss Martian and J'onn's long lost father in "Far From The Tree," so most of the week's superhero action took place away from National City. The big plot on the home front saw Alex and Maggie celebrating their engagement with a wedding shower. Maggie decided the time had come to try and reconcile with her homophobic parents, and she invited them to the shower. Maggie's dad Oscar made the trip, but he was unable to get over his prejudice for very long. In fact, he stormed out of the party as soon as he saw Maggie kiss Alex. The conversation between father and daughter that followed may have dropped a clue that something big was changed in the Supergirl timeline that hasn't yet been revealed.
Maggie confronted her father about why he refused to accept her as a gay woman on the verge of marrying the love of her life, and Oscar got mad and began to rant his reasons. He apparently came to Mexico as a child and spent years fighting for the respect of his peers, and it clearly didn't come easy for him as he was surrounded by people with prejudices against him as an immigrant. When Maggie argued that times had changed and she was accepted as a gay woman in National City, her father denied that times had really changed that much, saying this:
They're building a wall to keep us out!
It seems that Earth-38's version of the United States has a government attempting to build a wall between the U.S. and Mexico. While this line could simply be a Supergirl nod to the real-life political climate, it stands out rather glaringly from the in-universe political climate. The Earth-38 President of the United States is Olivia Marsdin, who is secretly an alien with good intentions. From her very first appearance on the series, Marsdin was working to give aliens rights just like humans on Earth with the Alien Amnesty Act, and Supergirl did not remove her from office at any point. In fact, the show sent Cat Grant to Washington D.C. to serve as President Marsdin's press secretary.
Basically, a wall between the United States and Mexico does not sound at all like something that would happen under President Marsdin as we know her. If Oscar had said "They want to build a wall" or "They hope to build a wall," we could assume that he was referring to people who are advocating for the construction of a wall. Since he said that they're building a wall, we have to assume that it's a project that's happening, and that almost certainly couldn't happen without the president on board.
It's hard to imagine anything happening in the original Supergirl timeline that would motivate the President Marsdin who wants to open the world for aliens to build a wall between countries. We have to wonder if Oscar's line about the wall is a sign that the Supergirl timeline has been altered without the audience knowing about it. Could this be a sign that Supergirl is going to explore the effects of time travel in Season 3?
Admittedly, superhero time travel has been pretty much limited to The Flash and Legends of Tomorrow in the Earth-1 branch of the Arrow-verse, but there's no reason why it can't happen on Supergirl. While shows in the Arrow-verse don't tend to introduce major plot points via quick hints that can be easily missed, Supergirl could be doing something more along the lines of the first few seasons of the Doctor Who revival and dropping hints that something is wrong in time. It would give a fresh take on time travel for superheroes on The CW, which could be interesting.
All of that said, Oscar's line about the wall really could have just been commentary about real life rather than a hint of anything in-universe. The villain of Season 3 hasn't been teased as having any connection to time travel, and anything that changes the president of the United States probably wouldn't be connected to a villain of the week. We shouldn't rule anything out at this point, but we also shouldn't take anything for granted. We'll have to wait and see.
New episodes of Supergirl air on Mondays at 8 p.m. ET on The CW.