Hotellings Law (https://www.uh.edu/engines/epi2692.htm) means that when there are two competitors on a spectrum, they will move closer and closer to one another to be as competitive as possible. Even passing beyond the other until they are both either side of the center.
You have two ice cream trucks on a 1D beach.
|-----1-----------2-|
Ice cream truck 2 captures all the business on its right, and 1 captures all the business (more) on it's left. Then they split the central. area 50:50.
|-----12------------|
Now 2 moves all the way to be next to 1, and takes all the central space (including what it used to have on the right.
|------21------------|
1 now comes to the side the grab almost all of the right hand side, surrendering the less valuable left.
|-------12-----------|
|--------21----------|
They'll now work back and forth until they're either side of the middle.
This is what you might imagine political parties would do and what they do in some countries. Something is stopping this happening in US politics and I would hazard a guess it's be because of a. primaries (were votes aren't evenly distributed along a 1D spectrum) and b. social cues (people are in politics for more than just winning votes).