In any other setting, this posturing would be only about Trump's image. He has made winning so key to his identity that he can't be seen to lose. So the only way he's allowed to lose is if his opponents cheat, and lie, and play games with the system (all while Trump tries the same, of course).
When cultivating his image takes the country's democratic system with it, though, it's unacceptable. It should be condemned by everybody -- but, of course, it won't be. Too many people have tied themselves to the Trump bandwagon, and either refuse to see the obvious, or refuse to ever condemn it, because to do so would be to admit culpability.