I think there can be a middle ground. The problem is that both parties have been overly obsessed with the border, without paying much attention to what's on the other side of the border. I think Biden and Harris are taking a different approach by reaching out directly to the governments in question - namely that of Mexico and the Northern Triangle countries (El Salvador, Guatemala, Honduras). We should have been doing that 20-30 years ago. If we had, we wouldn't even have this problem today.
I agree that there can be a middle ground (reached when opposing parties come together), but I disagree that a viable Third Party can form around a middle ground.
A Third Party isn't a middle ground. A Third Party is a
third perspective on issues and policies. The Trump movement was a Third Party movement that rejected ideas from both the right and the left and caused major changes in the Republican party. It's clear that a few Republicans don't like the change in their party and would like to go back to the way the Republican party was. I doubt that is feasible.
As for the border, Trump reached out directly to other governments. He made agreements with them, including processes for remote application of asylum. Biden threw **everything out** because it was
Trump border policy without regard to whether anything under Trump was good or bad!
The Biden-Harris approach is also not new. Their approach was tried before and failed - that's why Biden-Harris say, repeatedly, that Trump set them back. Trump got rid of the ineffective border policies of the past and worked on new border policies that were effective.
Will Biden-Harris be effective in their attempts? We'll see. So far, it's a disaster. Is there a third paradigm for the border that a Third Party can embody?