phill is right: Rand has not endorsed Trump at this time. Subtle point is that he has committed to endorse whoever the Republican nominee is, when that person is the nominee. Presumably that will be Trump, but it is not a certainty. The nominee will be known with certainty only after the first ballot at the National Convention, sometime after July 18. Who knows what might happen before then, however unlikely.
As it stands, the OP headline is inaccurate and misleading.
Just because the linked source of the OP used a similar misleading headline, doesn't justify using a misleading headline for the forum post.
A reasonable approach to reduce misunderstanding and unnecessary conflict would be to modify the headline to remove ambiguity, such as
Blog ("ETF News") claim: Rand Paul endorses Donald Trump
or even more clearly
Rand Paul reiterates previous commitment to endorse eventual Republican presidential nominee