A united front is a good idea. However, it is predicated on some kind of unity against fascism.
The centrist parties in Weimar Germany voted for the Enabling Act themselves. They had no principles against fascism, and were perfectly willing to enable fascism in order to advance parliamentary compromise.
In order for me to endorse a united front, I need to see indications that the center right faction actually opposes MAGA talking points on transgender people and immigration fervently and passionately. I haven't seen it this far.
Bernie and AOC understand fascism decently for US politicians. Hakeem Jefferies? Not so much.