A Republican Iowa state senator is suspending his party membership to protest presumptive presidential nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE.

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"I will not stand silent if the party of Lincoln and the end of slavery buckles under the racial bias of a bigot," David Johnson told The Des Moines Register Tuesday.

Johnson, who’s served in the Iowa legislature for 18 years as a Republican, said he made the decision to switch his voter registration to “no party” following Trump’s remarks regarding a Hispanic judge hearing a case against Trump University.

He has not decided whether he will continue to caucus with Republicans in the legislature.

Johnson, though, said he would register as a Republican again if the party mounts a last-ditch effort against its presumptive nominee.

“If Mr. Trump is the nominee, he becomes the standard bearer for a party that’s on the verge of breaking apart,” he said.

“He simply cannot unify the GOP. If there is a profound split, I’ll gladly re-join Republicans who are dedicated to equality and justice for all, and let Mr. Trump lead his supporters over the cliff.”