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.