Sen. Rand Paul, left, talks to his father, Rep. Ron Paul. The senator has joined his Texas congressman father frequently on the presidential campaign trail.
Ron Paul has told thousands of supporters that "we have infiltrated the Republican Party" in the name of defending liberty.
The GOP presidential hopeful and his son Rand addressed a boisterous rally Sunday outside the Texas Capitol.
The national Tea Party Express sponsored the event, which also featured senatorial candidate Ted Cruz.
Cruz is the tea party darling in a crowded field of Texas GOP candidates vying for their party's nomination to replace retiring Republican U.S. Sen. Kay Bailey Hutchison.
U.S. Sen. Rand Paul, a Kentucky Republican, has joined his Texas congressman father frequently on the campaign trail.
Texas holds its primary May 29. The elder Paul has recently attracted big crowds on college campuses in many states, but hasn't won any presidential caucuses or primaries.