I think in this situation the limit hasn't been reached; with 40+% of the nation's support, the Trump movement isn't fringe. Additionally, many voters intend to vote for him for politically expedient reasons, such as capturing 3 Supreme Court justice appointments for Republican judges.

Despite the objectively horrible viewpoints advanced by the Trump campaign, they do not approach David Duke's viewpoints.

From some points of view, pro-abortion advocacy is an unconscionable violation of human rights and outweighs religious (Muslim profiling) and racial (seizing remittances from Mexican nationals) concerns; it is a rationally-approached choice of a lesser of two evils.

This isn't strict cultural relativism; the argument has merit. I assert that including alternate viewpoints (but prohibiting bigoted / wrongful actions) strengthens institutions. The best demonstration of the strength of a world view is to accept discussion of alternate viewpoints. If we're right, we shouldn't be afraid of the alternative.