When tea-party activists rallied last weekend in Kentucky, their home-state hero, Sen. Rand Paul, wasn't invited. The event featured the tea-party candidate running for the Senate, while Mr. Paul is backing the incumbent, Sen. Mitch McConnell.

But leaders of FreedomWorks, the conservative group that organized the rally, still view Mr. Paul as an ally. In February, he joined their lawsuit over government phone surveillance. "That makes clear his willingness to shake up the political establishment," said FreedomWorks...