A trio of wealthy Texans have donated more than half of the money the pro-Republican super-PAC American Crossroads has received, according to a new study by the Center for Public Integrity.

Bob Perry, Harold Simmons and Robert Rowling have combined to donated $30.5 million to the group, more than half of the $56 million the total the group has raised since its creation.

All three are longtime Republican donors: Perry and Simmons provided the bulk of the money behind the controversial Swift Boat Veterans for Truth campaign, which attacked Sen. John KerryJohn Forbes KerryShould President Trump, like President Obama, forsake human rights in pursuit of the deal with a tyrant? GOP Senate report says Obama officials gave Iran access to US financial system Democrats conflicted over how hard to hit Trump on Iran MORE (D-Mass.) for some of his alleged actions while serving in Vietnam. Rowling was a major fund-raising bundler for President George W. Bush's (R) 2000 and 2004 elections.

Rove has deep ties with the Texas Republican donor community — he began his political career with Bush in Texas.

The study includes the money for American Crossroads but not Crossroads GPS, which because of its legal status does not have to disclose any of its donors.