In 1990, I got a rare compliment from my then-boss, Sen. Sam Nunn, for writing an introduction of Bill Clinton that included this quip: Bill Clinton is the first American politician to become a bright, rising star in three different decades. This was actually before Clinton earned the universal sobriquet of “comeback kid” for surviving a 1992 loss in New Hampshire and going on to win the presidency. But it captured the idea that his great potential had long been recognized.

Oddly enough, given his much-discussed youth (and even more youthful appearance), the newest 2016 official presidential candidate, Sen. Marco Rubio, is beginning to give off that same aroma of slightly marinated potential. In a very positive (if guarded) assessment of his candidacy, Erick Erickson emphasizes Rubio’s seniority in the Tea Party Movement as compared to Ted Cruz and Rand Paul. He also suggests Rubio has had to lay low lately until memories of his failed immigration reform gambit faded a bit.

That’s interesting in light of Nate Cohn’s more comprehensive evaluation of the Rubio candidacy, which speculates that the Floridian’s universally recognized potential won’t matter a whole lot in 2016 unless he makes a move, which is a lot easier said than done:

He enters the fray with surprisingly low support. Despite four years of national prominence, he has averaged 6 percent of the vote in primary polls over the last few months. That’s the same or worse than five candidates who are thought to have a much smaller chance of winning the nomination: Ted Cruz, Rand Paul, Ben Carson, Mike Huckabee and Chris Christie. Mr. Rubio is acceptable to many but, so far, the first choice of few….

Mr. Rubio’s struggle to break through is a powerful reminder that winning a presidential primary is not just about skill as a politician. It’s about positioning, and Mr. Rubio, at the moment, is in a much worse position than many assessments of his political talent would suggest. In basketball terms, he’s boxed out.

That’s mainly because his former mentor Jeb Bush has already nailed down most of the donors and home-state pols Rubio will ultimately have to attract. So while it’s easy to say that if Jebbie or Scott Walker fades, Rubio will have an open path to the nomination, this possibility seems to be beyond Rubio’s control.

The challenge for Mr. Rubio is heightened by the first two nominating contests, Iowa and New Hampshire, which are better understood as factional winnowing contests. The Iowa caucuses are deeply conservative — 47 percent of caucus-goers in 2012 identified as “very conservative” — and even more evangelical: 57 percent identified as born again or evangelical Christians. New Hampshire, on the other hand, is among the most moderate contests in the country: 47 percent of New Hampshire primary voters were self-identified moderates four years ago. It is not surprising that a candidate with broad but shallow appeal, like Mr. Rubio, has struggled to gain a strong foothold in either state.

To put it another way, if Jeb or Walker gets “winnowed” in Iowa or New Hampshire, somebody other than Marco Rubio will probably have already broken through, and Rubio may have been “winnowed” himself. Late-breaking candidacies are not a particularly common phenomenon in presidential nominating contests these days, and the GOP’s effort to tighten the calendar in 2016 makes it even more difficult to imagine a post-New Hamsphire “break-out” scenario.

The bottom line is that in politics as in so many other areas of life, “potential” is a great thing for a good while, but eventually the adjective “wasted” becomes all too easy to add to it. If Rubio has Clintonian reservoirs of resilience and imagination, I haven’t seen it yet.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.