Basic political math and mechanics:

[Stinky The Clown]

If you subtract a substantial portion of your base on the left, you need to make up for that reduction in numbers by adding an equal or greater number from elsewhere on the political spectrum, probably the right.

That's the math.

The mechanics are somewhat more complex. If, in moving right, you not only ignore and deride, but completely abandon the left, you open a gap that starts to resemble the size of the Democratic party during its lowest days. The Democratic party of that size eventually made it back to power.

Is there such a gap already? In the near future? I don't know. But some seem to be working on it.