Much has been made about the fact that Marco Rubio struggled last year and has thrived thus far in 2014. But while Rubio never seemed to have a specific rivalry with Rand Paul (who sparred with Chris Christie and more recently Ted Cruz), the two prospective 2016 presidential candidates seem to have their political fates connected in a way others don’t: one’s loss often accompanies the other’s gain. And this year, as Rubio recovers his footing it’s Paul who appears to be struggling. That’s been fairly consistent with the two Republicans’ shared term in the Senate thus far.

When Rubio burst onto the national GOP stage in 2010 in his Senate race against Charlie Crist, conservatives loved his message but fretted that his political persona was too dependent on that one message. The concern was voiced in August of that year by Weekly Standard editor Fred Barnes, who wrote: “In every appearance, including my interview with him in late July, he delivers the speech in whole or in part. There’s a reason for this: It’s an awfully good speech. It’s intensely patriotic and focused on how he’d like voters to see the choice they face in the election. It’s better than any speech I’ve heard from a Republican candidate or elected official in a long time. And Rubio delivers it passionately.”

That was all correct, but a question lingered: the right hoped Rubio would run for president sooner rather than later. Would his policy chops catch up, and could he build a record in time? The answer over the last couple of years, but especially this year so far, seems to be: Yes. His biggest setback has been his attempt to reform immigration law, but it showed at least that he wasn’t shy about putting forth detailed plans and advocating for them. Since immigration reform, he’s put out plans to tackle poverty, economic growth, higher education reform, and he hit his stride when attention turned to foreign affairs with Russia’s invasion of Ukraine and the popular unrest in Venezuela.

Rubio seemed to sputter in 2013 as Paul saw his moment in the sun. Paul’s famous filibuster not only won him plaudits from both sides of the aisle but also got his fellow Republican senators–Rubio among them–to appear on the chamber floor as supporting characters. Then the Edward Snowden affair happened, and Paul appeared to go from potential dark horse candidate in 2016 to the top tier. As the NSA domestic surveillance revelations were easily folded into the broader narrative of President Obama’s intrusive, big-government agenda, Paul took a step toward the front of the pack.

Part of Paul’s appeal was a term and a concept we’ve come to prize in American politics, with its ubiquity of television cameras and endless debates: authenticity. Paul came across as genuine and comfortable in his own skin, and he spoke confidently and fluently to any audience that would hear from him. It was no surprise that Paul and Christie developed something of a (brief) rivalry; neither pulls punches.

But Paul comes across as genuinely uncomfortable talking about foreign crises where the choice isn’t war or peace but something in the middle. Ukraine has made the contrast with Rubio clear, not just on policy but on the fact that events have shifted onto the latter’s turf. Paul’s TIME magazine piece on the appropriate American reaction to the Crimean crisis has already come in for some tough criticism, for example from National Review’s Patrick Brennan, who called Paul’s ideas “terrible or delusional.” But what caught my attention was more the stylistic clumsiness of the messaging–not that U.S. senators should be graded on whether their prose matches up to Tolstoy’s but to their own. In other words, Paul’s surefootedness is completely absent. For example:

America is a world leader, but we should not be its policeman or ATM.

At the end of the day, I still agree with former Chairman of the Joint Chiefs of Staff Mike Mullen — the greatest threat to America’s security is our national debt.

Russia, the Middle East or any other troubled part of the world should never make us forget that the U.S. is broke. We weaken our security and defenses when we print money out of thin air or borrow from other countries to allegedly support our own.

Like Dwight Eisenhower, I believe the U.S. can actually be stronger by doing less.

Like Ronald Reagan, particularly regarding Russia, I also believe, “Don’t mistake our reluctance for war for a lack of resolve.”

That’s just a sample, but much of the piece is written that way. It’s unlike Paul to speak without saying something, but he comes close to doing so on Ukraine. More than a week before Paul’s piece was published, Rubio published at Politico an immediate reaction to the crisis, whose applicability showed he was either prepared for the Russian action or he didn’t need to be to know how to react.

The issues underpinning Rubio and Paul’s fortunes demonstrate something else: unlike Christie’s “bridgegate,” which involved his staff, for Paul and Rubio events beyond their control have exerted upward or downward pressure on them–in Paul’s case, the NSA revelations and for both the crisis in Ukraine (and to a lesser extent Venezuela). It shows the degree of uncertainty and luck in the process. But then again, that’s often how it is in the White House too.