Sen. Rand Paul was supposed to be a more politically savvy version of his father, former Texas congressman and presidential candidate Ron Paul.

The senior Paul energized a subset of the Republican Party, but the younger Paul was supposed to be a more mainstream advocate for limited government and a non-interventionist foreign policy.

The Kentucky senator has even been touted as one of the leading candidates for the 2016 Republican presidential nomination.

Yet time and again, he has shown why he shouldn't be taken seriously.

The latest controversy surrounding Paul, which has been detailed in a series of stories at BuzzFeed by Andrew Kaczynski, involves a pattern of plagiarism in which he has cut and pasted large sections of his writings from other sources without proper attribution.

Instead of simply owning up to it, Paul lashed out at the media: “I'm being criticized for not having proper attribution, and yet they are able to write stuff that if I were their journalism teacher in college, I would fail them,” Paul told National Review's Robert Costa.

Paul's dismissive tone recalls another incident earlier this year when it was revealed that a staffer who had helped write one of his books had a long history of pro-confederate sympathies.

I have no doubt that his core supporters will stick with Paul through his plagiarism scandal, just as his father Ron's passionate fans stuck with him, despite a troubling history of publishing racist newsletters and a tendency to make outrageous statements and claims.

But to win the nomination in 2016, Rand Paul has to expand his appeal beyond this core group. He won't be able to accomplish that if he continues to behave like an amateur.