A group backing Republican Ted Cruz has compared Donald Trump to a slave-owner, because he no longer opposes same-sex marriage.

The billionaire reality TV star-turned-politician is currently leading the Republican Presidential race.

He declared last year that opposing same-sex marriage is a “dead issue” – though he has murky stances on a number of other LGBT issues.

The National Organisation for Marriage has thrown its weight behind Trump’s rival Ted Cruz – who wants to void all same-sex marriages – and posted a lengthy diatribe comparing Trump to a slaver.

The group’s President Brian Brown wrote: “Donald Trump does not support a constitutional amendment to restore marriage to our laws. Worse, he has publicly abandoned the fight for marriage.

“When the US Supreme Court issued their illegitimate ruling redefining marriage, Trump promptly threw in the towel with these comments on MSNBC: ‘You have to go with it. The decision’s been made, and that is the law of the land.;

“Think about the implications of Donald Trump’s comments. By his reasoning, the nation would ‘have to go with’ slavery as ‘the law of the land’ once the Supreme Court issued their illegitimate Dred Scott decision.

“But the nation didn’t go along with this manifestly immoral, anti-constitutional ruling on slavery.

“Fortunately, we had a political leader, Abraham Lincoln, who was willing to lead a principled fight for the dignity of every human being, and slavery was eventually repudiated.”

The group added of Cruz: “That in a nutshell is the difference between Ted Cruz and Donald Trump when it comes to marriage. Ted Cruz will be a champion for marriage while Donald Trump has abandoned the fight.

“In fact, Ted Cruz has already proven himself to be a champion for marriage by authorizing a proposed constitutional amendment preserving the right of states to define marriage as the union of one man and one woman.

“He also has co-sponsored federal legislation, the First Amendment Defense Act, to protect people who believe in traditional marriage from being punished by government for living out their beliefs concerning marriage in their daily lives and at work.”

Despite once-friendly relations between the Cruz and Trump campaigns, the pair’s relationship has soured significantly.

Donald Trump recently branded Senator Cruz a “hypocrite” for opposing LGBT rights while taking money from gay donors.