But the upside goes both ways on this one: while Paul is a helpful validator for Romney, endorsing Romney also gives Paul a level of mainstream credibility he lacked during his 2010 Senate campaign. It shows he’s willing to be a team player when it counts, and puts him on the safe side of any speculation over a third-party libertarian push.

And that could be crucially important or Paul if he decides to seek the White House himself in 2016 or beyond – as any number of operatives believe he hopes to do.

“Rand’s endorsement of GOP nominee Mitt Romney clearly shows that in spite of those who try to marginalize him, he has keen set of political instincts and is very much aware that a successful national run will require more than just his father’s loyal following,” said one Republican strategist close to Paul-world.