I don't claim to know for certain what MBTI type Ron Paul is, but there is no way he is an ESTJ.
Paul does not seek order or continuity. He seeks to purge the system of features that have been there for over a hundred years in some cases. He is not a joiner. He has been saying the same things for as long as I've been alive, and in recent years been surprised that people just started to listen and join him. He is pretty much computer illiterate and has almost nothing to do with the fan base that has grown around him since starting his 2008 presidential campaign. He does not have a strong sense of orthodoxy, and decries most of what is normal as injustice. He does oppose entitlements and has nothing against a strong work ethic, but I've never really heard him decry laziness either. An ESTJ would likely denigrate those who don't work hard enough, whereas he has no problem with those content to live with what their laziness allows without demanding to be subsidized. He doesn't seem to think much of anyone having power or prestige. ESTJs are often outspoken and opinionated, but I would hardly call them people of principle more than other types. They don't really break things down into principles, they just occasionally explode with raw Fi.
I've seen some sites have Ron Paul listed as an ENTJ, but seems absolutely nothing like any ENTJ I know. A lot of politicians are extraverts, but I do not believe that he is one of them. He is generally a rather private man, and seemed taken by surprise by his sudden rise in popularity a few years ago.
I've seen other sites claim that he is an INTJ, which seems far more likely but not certain. He seems to have quite a bit in common with the supposedly INTJ Calvin Coolidge, but not much with less introverted (and confirmed) INTJ Hilary Clinton. My INTJ father thinks very different from Paul, and considers the man crazy.
Ron does tend to focus more on trying to understand why things are as they are and addressing the root causes rather than finding the most efficient means of reaching goals. I could easily see him as using more Ti than Te.
I could definitely see him as an INFJ, but could not rule out INTJ or INTP completely.
Incidentally, by best real life INFJ friend is a very strong Ron Paul supporter, although she personally leans towards the more extreme wing of the Libertarian Party. She used to call herself a Christian-Anarcho-Capitalist, but more recently prefers the term Panarchist. (She was really proud of his son Rand's senate victor in the state where she was born.)
I like Ron Paul much more than most politicians, but am not one of his diehard followers. He has too strong an opposition to illegal immigration (even if it is weaker than the republican norm), when a libertarian really should oppose all the laws making such immigration illegal in the first place. If I were him I would bring up not only the fact that we are fighting undeclared wars, but the fact that the Kellog-Briand Pact would make them illegal even if Congress had followed the proper constitutional procedures. While I think we would have been better off sticking with the silver standard (the gold standard causes significant problems as the supply could keep up with population growth and meant de facto deflation, at a time when bimetallism would have worked quite well), rushing to abolish the Fed would probably cause more problems than it fixes. I would not cut taxes as much as as quickly as he would, since I don't see how we could ever pay down the national debt if we do so. I have a significant Geoist influence, so I would support raising taxes on natural capital (both in the form of land value taxes and Pigouvian "Green Taxes" on pollution) and paying Citizen Dividends rather than cutting off the poor from government assistance altogether.
(I really dislike his son Rand Paul, in large part because he supports protecting big business from being held accountable for the environmental damage they cause. Ron Paul wants to get rid of limits on tort cases were property owners sue polluters. I personally don't think this is enough (given how corporations keep better lawyers on retainer than most private citizens could ever afford), but it is much better than Rand's plan to limit such torts so strictly that it is almost impossible to punish polluters. His college shenanigans also show his character in a negative light, and when watching him speak I just get the vibe that he is kind of an asshole.)