Parkhurst was one of several at the summit to echo that sentiment. It was a dramatic demonstration of a dynamic political watchers have speculated about—Cruz's ability to steal Paul's thunder if both seek the 2016 GOP nomination.

And seeking the nomination is something both men seem inclined to pursue. Both headlined weekend events with the New Hampshire Republican Party in addition to appearing at the summit, which was sponsored by Citizens United and Americans for Prosperity. (Yes, the Supreme Court plaintiff that helped deregulate campaign finance and the Koch Brothers' political nonprofit collaborated—a liberal conspiracy theory come to life.) Cruz finished his speech by asking audience members to subscribe to text-message alerts for his "movement," a tech-savvy means of building a list of grassroots supporters.

Paul's father, former Representative Ron Paul, came in second to Mitt Romney in the 2012 New Hampshire primary, and the senator's strategists see New Hampshire as a potential stronghold. With his appeal to civil libertarians and idealistic young activists, he has a built-in base of support that is loyal only to him.

But for Rand Paul to be more than a niche candidate and win the nomination, he must attract support from other, more traditionally Republican segments—starting with the Tea Party, of which he's positioned himself as a leader, authoring a book called The Tea Party Goes to Washington and delivering the Tea Party response to President Obama's State of the Union address in 2013.

But Cruz, who came to the Senate two years after Paul, appears to be muscling him out of first place in Tea Partiers' hearts. Where Paul calls himself a "libertarian Republican," Cruz touts his full-spectrum conservatism on fiscal, social, and foreign policy. Cruz aggressively championed the push to defund Obamacare that helped lead to last fall's government shutdown (Paul also backed it, but tepidly), an act that made him a pariah in Washington but a hero to the grassroots. Paul got lots of attention for staging a 13-hour filibuster on the Obama Administration's use of drones last March; Cruz transparently copied the tactic with an even longer speech on Obamacare in September.

The contrast between those two speeches is instructive. Paul's was on a pet issue dear to libertarians—but one that is divisive within the party and not a top concern for the GOP base. His action actually got results in the form of a letter from the administration. Cruz's speech was pointless—he couldn't delay the Senate vote in question, and the only tangible result was attention for Cruz—and it may not have technically been a real filibuster. But by crusading against Obamacare, he hit the hottest button for conservative activists.

A similar contrast was on display in New Hampshire, where the decidedly Tea Party crowd also gave a warm welcome to right-wing gadfly Donald Trump and talk-radio host Mike Huckabee, both of whom are also flirting with presidential runs. Potential candidates with more establishment appeal, such as former Florida Governor Jeb Bush and New Jersey Governor Chris Christie, were not on the schedule; Trump castigated Bush for his sympathetic view of illegal immigrants, and multiple speakers, including Cruz, bashed the Common Core educational standards, which Bush vocally supports. Scott Brown, the former Massachusetts senator now running in New Hampshire, also declined to appear at the event.