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Santorum's endorsement comes after Sens. Jon Kyl and John McCainJohn McCainSenate panel votes to confirm Tillerson Overnight Defense: Trump nominates Air Force secretary | Senate clears CIA director | Details on first drone strike under Trump McCain: Trump's withdrawal from TPP a 'serious mistake' MORE, both Arizona Republicans, endorsed Flake in the increasingly contentious primary. And the Club for Growth, the prominent conservative organization, also pledged to spend half a million dollars on advertisements supporting the Arizona lawmaker.

Cardon now hopes that Santorum can rally Tea Party conservatives in the state. A poll released late last month by Magellan Strategies found Flake with a 22-point lead in the primary battle, despite Cardon's million-dollar ad blitz against the six-term congressman.