Please define "open borders", and tell me which politicians support that. Certainly neither Democrats nor Republican consider it part of their party's goals:

"Trump has inaccurately accused opponents from both parties, but especially Democrats, of supporting open borders, claiming they would allow "criminals" and "terrorists" to enter the U.S. undeterred. Democratic leaders have pushed back, pointing out that they support secure borders, and as Sanders said, wanted comprehensive immigration reform." - https://www.newsweek.com/bernie-sanders-open-borders-poverty...

While we know that the Republican donors Charles and David Koch support open borders, as the Newsweek article quotes: "I would let everybody in who comes here to contribute, and no one who wants to come here to do harm".

Open borders are what we have between the states. Open borders are like between England and Scotland.

Very few places - Svalbard being the only one I know of - have open borders where anyone can enter the country, without visa or other permit, and even become citizens that way.

I don't think any major political party has that sort of open border as a goal, left or right.