Trump declines backing republican nominee

I think you may be mistaken. While Donald Trump has been known to make unconventional statements and decisions, I'm not aware of any instance where he has declined to back a Republican nominee.

In fact, as the 45th President of the United States, Trump has been a prominent figure in the Republican Party and has often used his platform to support and endorse Republican candidates. He has also been known to use his Twitter account to express his opinions and endorsements, often with significant impact on the political landscape.

If you're thinking of a specific instance where Trump declined to back a Republican nominee, I'd be happy to help you fact-check it.