Please pay attention and read this carefully.
Trump PUBLICLY ENDORSED BOTH MCCAIN AN ROMNEY!!!
His words were: "The fact is that Obama went limping across the finish line. He should have chosen Hillary, it would have been a much different race, I believe. Right now, it looks to me like McCain is probably winning."
And Trump only likes winners. Perhaps that is why, even as a registered Democrat at the time and a big fan of Hillary, he endorsed McCain.
As for endorsing Romney -- Trump switched to the Republican party in 2011. Romney was and is a functional Democrat registered as a Republican. Trump's endorsement of Romney was par for the course.