Let's not be pollyannaish about Rand Paul in 2020
Would the Republican Party be headed toward victory if we had nominated Rand Paul? I contend that any of the other Republicans would be crushing Hillary Clinton right now, but a case can be made for Paul. While it is true that Paul had a unique opportunity to expand the Republican voter base, we should not be unrealistically optimistic about Paul's chances, either what they would have been this year or what they will be in 2020.
First, there are a number of Republicans turned off by libertarianism. There are the more old-school Republicans, of course, but many Christians of all ages are wary of the social stances libertarianism takes - specifically on drug decriminalization. Paul would have had some problems unifying the GOP base had he won the nomination, and if he is the nominee in 2020 he will face that same problem.
The biggest problem for Paul would be interventionists within the party, because of his skepticism of U.S. military adventures around the world. That is the biggest complaint I hear from even libertarian-leaning Republicans who believe we as a nation have a moral obligation to project power in order to defend and promote our values around the world. When John McCain said back in 2013 that he would consider voting for Hillary Clinton over Paul, the fact that Clinton is much more willing than Paul to commit military forces was one of the main reasons behind that statement.
Paul is also going to have trouble convincing "law and order" types in the Republican base to vote for him in order to win a primary or to get them motivated in a general election. Republicans are very wary of candidates who are perceived as "soft on crime," and that label has been applied to Paul. He will need to convince Republican voters that he will be tough on crime while also making the case that overcriminalizing everything, unduly harsh punishments and restrictions on due process are actually anti-conservative positions that are unfair and give government too much power.
I would have voted for Paul in a femtosecond, and I will vote for him if he is the 2020 nominee, but he does face some challenges. Paul will need to overcome these challenges if he is going to be a serious contender for President of these United States in four years. Republicans who would love to see a President Paul cannot ignore or brush aside these challenges. If they want him to win (either the nomination or the Presidency) they must be realistic and not allow themselves to be blindsided by those challenges. Now is the time to start addressing them.